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I have to find the best algorithm to define pairing between the items from two lists as in the figure. The pair is valid only if the number of node in list A is lower than number of node in list B and there are no crosses between links. The quality of the matching algorithm is determined by the total number of links.
I firstly tried to use a very simple algorithm: take a node in the list A and then look for the first node in list B that is higher than the former. The second figure shows a test case where this algorithm is not the best one.
Simple back-tracking can work (it may not be optimal, but it will certainly work).
For each legal pairing A[i], B[j], there are two choices:
take it, and make it illegal to try to pair any A[x], B[y] with x>i and y<j
not take it, and look at other possible pairs
By incrementally adding legal pairs to a bunch of pairs, you will eventually exhaust all legal pairings down a path. The number of valid pairings in a path is what you seek to maximize, and this algorithm will look at all possible answers and is guaranteed to work.
Pseudocode:
function search(currentPairs):
bestPairing = currentPairs
for each currently legal pair:
nextPairing = search(copyOf(currentPairs) + this pair)
if length of nextPairing > length of bestPairing:
bestPairing = nextPairing
return bestPairing
Initially, you will pass an empty currentPairs. Searching for legal pairs is the tricky part. You can use 3 nested loops that look at all A[x], B[y], and finally, if A[x] < B[y], look against all currentPairs to see if the there is a crossing line (the cost of this is roughly O(n^3)); or you can use a boolean matrix of valid pairings, which you update at each level (less computation time, down to O(n^2) - but more expensive in terms of memory)
Here a Java implementation.
For convinience I first build a map with the valid choices for each entry of list(array) a to b.
Then I loop throuough the list, making no choice and the valid choices for a connection to b.
Since you cant go back without crossing the existing connections I keep track of the maximum assigned in b.
Works at least for the two examples...
public class ListMatcher {
private int[] a ;
private int[] b ;
private Map<Integer,List<Integer>> choicesMap;
public ListMatcher(int[] a, int[] b) {
this.a = a;
this.b = b;
choicesMap = makeMap(a,b);
}
public Map<Integer,Integer> solve() {
Map<Integer,Integer> solution = new HashMap<>();
return solve(solution, 0, -1);
}
private Map<Integer,Integer> solve(Map<Integer,Integer> soFar, int current, int max) {
// done
if (current >= a.length) {
return soFar;
}
// make no choice from this entry
Map<Integer, Integer> solution = solve(new HashMap<>(soFar),current+1, max);
for (Integer choice : choicesMap.get(current)) {
if (choice > max) // can't go back
{
Map<Integer,Integer> next = new HashMap<>(soFar);
next.put(current, choice);
next = solve(next, current+1, choice);
if (next.size() > solution.size()) {
solution = next;
}
}
}
return solution;
}
// init possible choices
private Map<Integer, List<Integer>> makeMap(int[] a, int[] b) {
Map<Integer,List<Integer>> possibleMap = new HashMap<>();
for(int i = 0; i < a.length; i++) {
List<Integer> possible = new ArrayList<>();
for(int j = 0; j < b.length; j++) {
if (a[i] < b[j]) {
possible.add(j);
}
}
possibleMap.put(i, possible);
}
return possibleMap;
}
public static void main(String[] args) {
ListMatcher matcher = new ListMatcher(new int[]{3,7,2,1,5,9,2,2},new int[]{4,5,10,1,12,3,6,7});
System.out.println(matcher.solve());
matcher = new ListMatcher(new int[]{10,1,1,1,1,1,1,1},new int[]{2,2,2,2,2,2,2,101});
System.out.println(matcher.solve());
}
}
Output
(format: zero-based index_in_a=index_in_b)
{2=0, 3=1, 4=2, 5=4, 6=5, 7=6}
{1=0, 2=1, 3=2, 4=3, 5=4, 6=5, 7=6}
Your solution isn't picked because the solutions making no choice are picked first.
You can change this by processing the loop first...
Thanks to David's suggestion, I finally found the algorithm. It is an LCS approach, replacing the '=' with an '>'.
Recursive approach
The recursive approach is very straightforward. G and V are the two vectors with size n and m (adding a 0 at the beginning of both). Starting from the end, if last from G is larger than last from V, then return 1 + the function evaluated without the last item, otherwise return max of the function removing last from G or last from V.
int evaluateMaxRecursive(vector<int> V, vector<int> G, int n, int m) {
if ((n == 0) || (m == 0)) {
return 0;
}
else {
if (V[n] < G[m]) {
return 1 + evaluateMaxRecursive(V, G, n - 1, m - 1);
} else {
return max(evaluateMaxRecursive(V, G, n - 1, m), evaluateMaxRecursive(V, G, n, m - 1));
}
}
};
The recursive approach is valid with small number of items, due to the re-evaluation of same lists that occur during the loop.
Non recursive approach
The non recursive approach goes in the opposite direction and works with a table that is filled in after having clared to 0 first row and first column. The max value is the value in the bottom left corner of the table
int evaluateMax(vector<int> V, vector<int> G, int n, int m) {
int** table = new int* [n + 1];
for (int i = 0; i < n + 1; ++i)
table[i] = new int[m + 1];
for (int i = 0; i < n + 1; i++)
for (int t = 0; t < m + 1; t++)
table[i][t] = 0;
for (int i = 1; i < m + 1; i++)
for (int t = 1; t < n + 1; t++) {
if (G[i - 1] > V[t - 1]) {
table[t] [i] = 1 + table[t - 1][i - 1];
}
else {
table[t][i] = max(table[t][i - 1], table[t - 1][i]);
}
}
return table[n][m];
}
You can find more details here LCS - Wikipedia
If the input is 'abba' then the possible palindromes are a, b, b, a, bb, abba.
I understand that determining if string is palindrome is easy. It would be like:
public static boolean isPalindrome(String str) {
int len = str.length();
for(int i=0; i<len/2; i++) {
if(str.charAt(i)!=str.charAt(len-i-1) {
return false;
}
return true;
}
But what is the efficient way of finding palindrome substrings?
This can be done in O(n), using Manacher's algorithm.
The main idea is a combination of dynamic programming and (as others have said already) computing maximum length of palindrome with center in a given letter.
What we really want to calculate is radius of the longest palindrome, not the length.
The radius is simply length/2 or (length - 1)/2 (for odd-length palindromes).
After computing palindrome radius pr at given position i we use already computed radiuses to find palindromes in range [i - pr ; i]. This lets us (because palindromes are, well, palindromes) skip further computation of radiuses for range [i ; i + pr].
While we search in range [i - pr ; i], there are four basic cases for each position i - k (where k is in 1,2,... pr):
no palindrome (radius = 0) at i - k
(this means radius = 0 at i + k, too)
inner palindrome, which means it fits in range
(this means radius at i + k is the same as at i - k)
outer palindrome, which means it doesn't fit in range
(this means radius at i + k is cut down to fit in range, i.e because i + k + radius > i + pr we reduce radius to pr - k)
sticky palindrome, which means i + k + radius = i + pr
(in that case we need to search for potentially bigger radius at i + k)
Full, detailed explanation would be rather long. What about some code samples? :)
I've found C++ implementation of this algorithm by Polish teacher, mgr Jerzy Wałaszek.
I've translated comments to english, added some other comments and simplified it a bit to be easier to catch the main part.
Take a look here.
Note: in case of problems understanding why this is O(n), try to look this way:
after finding radius (let's call it r) at some position, we need to iterate over r elements back, but as a result we can skip computation for r elements forward. Therefore, total number of iterated elements stays the same.
Perhaps you could iterate across potential middle character (odd length palindromes) and middle points between characters (even length palindromes) and extend each until you cannot get any further (next left and right characters don't match).
That would save a lot of computation when there are no many palidromes in the string. In such case the cost would be O(n) for sparse palidrome strings.
For palindrome dense inputs it would be O(n^2) as each position cannot be extended more than the length of the array / 2. Obviously this is even less towards the ends of the array.
public Set<String> palindromes(final String input) {
final Set<String> result = new HashSet<>();
for (int i = 0; i < input.length(); i++) {
// expanding even length palindromes:
expandPalindromes(result,input,i,i+1);
// expanding odd length palindromes:
expandPalindromes(result,input,i,i);
}
return result;
}
public void expandPalindromes(final Set<String> result, final String s, int i, int j) {
while (i >= 0 && j < s.length() && s.charAt(i) == s.charAt(j)) {
result.add(s.substring(i,j+1));
i--; j++;
}
}
So, each distinct letter is already a palindrome - so you already have N + 1 palindromes, where N is the number of distinct letters (plus empty string). You can do that in single run - O(N).
Now, for non-trivial palindromes, you can test each point of your string to be a center of potential palindrome - grow in both directions - something that Valentin Ruano suggested.
This solution will take O(N^2) since each test is O(N) and number of possible "centers" is also O(N) - the center is either a letter or space between two letters, again as in Valentin's solution.
Note, there is also O(N) solution to your problem, based on Manacher's algoritm (article describes "longest palindrome", but algorithm could be used to count all of them)
I just came up with my own logic which helps to solve this problem.
Happy coding.. :-)
System.out.println("Finding all palindromes in a given string : ");
subPal("abcacbbbca");
private static void subPal(String str) {
String s1 = "";
int N = str.length(), count = 0;
Set<String> palindromeArray = new HashSet<String>();
System.out.println("Given string : " + str);
System.out.println("******** Ignoring single character as substring palindrome");
for (int i = 2; i <= N; i++) {
for (int j = 0; j <= N; j++) {
int k = i + j - 1;
if (k >= N)
continue;
s1 = str.substring(j, i + j);
if (s1.equals(new StringBuilder(s1).reverse().toString())) {
palindromeArray.add(s1);
}
}
}
System.out.println(palindromeArray);
for (String s : palindromeArray)
System.out.println(s + " - is a palindrome string.");
System.out.println("The no.of substring that are palindrome : "
+ palindromeArray.size());
}
Output:-
Finding all palindromes in a given string :
Given string : abcacbbbca
******** Ignoring single character as substring palindrome ********
[cac, acbbbca, cbbbc, bb, bcacb, bbb]
cac - is a palindrome string.
acbbbca - is a palindrome string.
cbbbc - is a palindrome string.
bb - is a palindrome string.
bcacb - is a palindrome string.
bbb - is a palindrome string.
The no.of substring that are palindrome : 6
I suggest building up from a base case and expanding until you have all of the palindomes.
There are two types of palindromes: even numbered and odd-numbered. I haven't figured out how to handle both in the same way so I'll break it up.
1) Add all single letters
2) With this list you have all of the starting points for your palindromes. Run each both of these for each index in the string (or 1 -> length-1 because you need at least 2 length):
findAllEvenFrom(int index){
int i=0;
while(true) {
//check if index-i and index+i+1 is within string bounds
if(str.charAt(index-i) != str.charAt(index+i+1))
return; // Here we found out that this index isn't a center for palindromes of >=i size, so we can give up
outputList.add(str.substring(index-i, index+i+1));
i++;
}
}
//Odd looks about the same, but with a change in the bounds.
findAllOddFrom(int index){
int i=0;
while(true) {
//check if index-i and index+i+1 is within string bounds
if(str.charAt(index-i-1) != str.charAt(index+i+1))
return;
outputList.add(str.substring(index-i-1, index+i+1));
i++;
}
}
I'm not sure if this helps the Big-O for your runtime, but it should be much more efficient than trying each substring. Worst case would be a string of all the same letter which may be worse than the "find every substring" plan, but with most inputs it will cut out most substrings because you can stop looking at one once you realize it's not the center of a palindrome.
I tried the following code and its working well for the cases
Also it handles individual characters too
Few of the cases which passed:
abaaa --> [aba, aaa, b, a, aa]
geek --> [g, e, ee, k]
abbaca --> [b, c, a, abba, bb, aca]
abaaba -->[aba, b, abaaba, a, baab, aa]
abababa -->[aba, babab, b, a, ababa, abababa, bab]
forgeeksskeegfor --> [f, g, e, ee, s, r, eksske, geeksskeeg,
o, eeksskee, ss, k, kssk]
Code
static Set<String> set = new HashSet<String>();
static String DIV = "|";
public static void main(String[] args) {
String str = "abababa";
String ext = getExtendedString(str);
// will check for even length palindromes
for(int i=2; i<ext.length()-1; i+=2) {
addPalindromes(i, 1, ext);
}
// will check for odd length palindromes including individual characters
for(int i=1; i<=ext.length()-2; i+=2) {
addPalindromes(i, 0, ext);
}
System.out.println(set);
}
/*
* Generates extended string, with dividors applied
* eg: input = abca
* output = |a|b|c|a|
*/
static String getExtendedString(String str) {
StringBuilder builder = new StringBuilder();
builder.append(DIV);
for(int i=0; i< str.length(); i++) {
builder.append(str.charAt(i));
builder.append(DIV);
}
String ext = builder.toString();
return ext;
}
/*
* Recursive matcher
* If match is found for palindrome ie char[mid-offset] = char[mid+ offset]
* Calculate further with offset+=2
*
*
*/
static void addPalindromes(int mid, int offset, String ext) {
// boundary checks
if(mid - offset <0 || mid + offset > ext.length()-1) {
return;
}
if (ext.charAt(mid-offset) == ext.charAt(mid+offset)) {
set.add(ext.substring(mid-offset, mid+offset+1).replace(DIV, ""));
addPalindromes(mid, offset+2, ext);
}
}
Hope its fine
public class PolindromeMyLogic {
static int polindromeCount = 0;
private static HashMap<Character, List<Integer>> findCharAndOccurance(
char[] charArray) {
HashMap<Character, List<Integer>> map = new HashMap<Character, List<Integer>>();
for (int i = 0; i < charArray.length; i++) {
char c = charArray[i];
if (map.containsKey(c)) {
List list = map.get(c);
list.add(i);
} else {
List list = new ArrayList<Integer>();
list.add(i);
map.put(c, list);
}
}
return map;
}
private static void countPolindromeByPositions(char[] charArray,
HashMap<Character, List<Integer>> map) {
map.forEach((character, list) -> {
int n = list.size();
if (n > 1) {
for (int i = 0; i < n - 1; i++) {
for (int j = i + 1; j < n; j++) {
if (list.get(i) + 1 == list.get(j)
|| list.get(i) + 2 == list.get(j)) {
polindromeCount++;
} else {
char[] temp = new char[(list.get(j) - list.get(i))
+ 1];
int jj = 0;
for (int ii = list.get(i); ii <= list
.get(j); ii++) {
temp[jj] = charArray[ii];
jj++;
}
if (isPolindrome(temp))
polindromeCount++;
}
}
}
}
});
}
private static boolean isPolindrome(char[] charArray) {
int n = charArray.length;
char[] temp = new char[n];
int j = 0;
for (int i = (n - 1); i >= 0; i--) {
temp[j] = charArray[i];
j++;
}
if (Arrays.equals(charArray, temp))
return true;
else
return false;
}
public static void main(String[] args) {
String str = "MADAM";
char[] charArray = str.toCharArray();
countPolindromeByPositions(charArray, findCharAndOccurance(charArray));
System.out.println(polindromeCount);
}
}
Try out this. Its my own solution.
// Maintain an Set of palindromes so that we get distinct elements at the end
// Add each char to set. Also treat that char as middle point and traverse through string to check equality of left and right char
static int palindrome(String str) {
Set<String> distinctPln = new HashSet<String>();
for (int i=0; i<str.length();i++) {
distinctPln.add(String.valueOf(str.charAt(i)));
for (int j=i-1, k=i+1; j>=0 && k<str.length(); j--, k++) {
// String of lenght 2 as palindrome
if ( (new Character(str.charAt(i))).equals(new Character(str.charAt(j)))) {
distinctPln.add(str.substring(j,i+1));
}
// String of lenght 2 as palindrome
if ( (new Character(str.charAt(i))).equals(new Character(str.charAt(k)))) {
distinctPln.add(str.substring(i,k+1));
}
if ( (new Character(str.charAt(j))).equals(new Character(str.charAt(k)))) {
distinctPln.add(str.substring(j,k+1));
} else {
continue;
}
}
}
Iterator<String> distinctPlnItr = distinctPln.iterator();
while ( distinctPlnItr.hasNext()) {
System.out.print(distinctPlnItr.next()+ ",");
}
return distinctPln.size();
}
Code is to find all distinct substrings which are palindrome.
Here is the code I tried. It is working fine.
import java.util.HashSet;
import java.util.Set;
public class SubstringPalindrome {
public static void main(String[] args) {
String s = "abba";
checkPalindrome(s);
}
public static int checkPalindrome(String s) {
int L = s.length();
int counter =0;
long startTime = System.currentTimeMillis();
Set<String> hs = new HashSet<String>();
// add elements to the hash set
System.out.println("Possible substrings: ");
for (int i = 0; i < L; ++i) {
for (int j = 0; j < (L - i); ++j) {
String subs = s.substring(j, i + j + 1);
counter++;
System.out.println(subs);
if(isPalindrome(subs))
hs.add(subs);
}
}
System.out.println("Total possible substrings are "+counter);
System.out.println("Total palindromic substrings are "+hs.size());
System.out.println("Possible palindromic substrings: "+hs.toString());
long endTime = System.currentTimeMillis();
System.out.println("It took " + (endTime - startTime) + " milliseconds");
return hs.size();
}
public static boolean isPalindrome(String s) {
if(s.length() == 0 || s.length() ==1)
return true;
if(s.charAt(0) == s.charAt(s.length()-1))
return isPalindrome(s.substring(1, s.length()-1));
return false;
}
}
OUTPUT:
Possible substrings:
a
b
b
a
ab
bb
ba
abb
bba
abba
Total possible substrings are 10
Total palindromic substrings are 4
Possible palindromic substrings: [bb, a, b, abba]
It took 1 milliseconds
Given an unsorted array, find the max j - i difference between indices such that j > i and a[j] > a[i] in O(n). I am able to find j and i using trivial methods in O(n^2) complexity but would like to know how to do this in O(n)?
Input: {9, 2, 3, 4, 5, 6, 7, 8, 18, 0}
Output: 8 ( j = 8, i = 0)
Input: {1, 2, 3, 4, 5, 6}
Output: 5 (j = 5, i = 0)
For brevity's sake I am going to assume all the elements are unique. The algorithm can be extended to handle non-unique element case.
First, observe that if x and y are your desired max and min locations respectively, then there can not be any a[i] > a[x] and i > x, and similarly, no a[j] < a[y] and j < y.
So we scan along the array a and build an array S such that S[i] holds the index of the minimum element in a[0:i]. Similarly an array T which holds the index of the maximum element in a[n-1:i] (i.e., backwards).
Now we can see that a[S[i]] and a[T[i]] are necessarily decreasing sequences, since they were the minimum till i and maximum from n till i respectively.
So now we try to do a merge-sort like procedure. At each step, if a[S[head]] < a[T[head]], we pop off an element from T, otherwise we pop off an element from S. At each such step, we record the difference in the head of S and T if a[S[head]] < a[T[head]]. The maximum such difference gives you your answer.
EDIT: Here is a simple code in Python implementing the algorithm.
def getMaxDist(arr):
# get minima going forward
minimum = float("inf")
minima = collections.deque()
for i in range(len(arr)):
if arr[i] < minimum:
minimum = arr[i]
minima.append((arr[i], i))
# get maxima going back
maximum = float("-inf")
maxima = collections.deque()
for i in range(len(arr)-1,0,-1):
if arr[i] > maximum:
maximum = arr[i]
maxima.appendleft((arr[i], i))
# do merge between maxima and minima
maxdist = 0
while len(maxima) and len(minima):
if maxima[0][0] > minima[0][0]:
if maxima[0][1] - minima[0][1] > maxdist:
maxdist = maxima[0][1] - minima[0][1]
maxima.popleft()
else:
minima.popleft()
return maxdist
Let's make this simple observation: If we have 2 elements a[i], a[j] with i < j and a[i] < a[j] then we can be sure that j won't be part of the solution as the first element (he can be the second but that's a second story) because i would be a better alternative.
What this tells us is that if we build greedily a decreasing sequence from the elements of a the left part of the answer will surely come from there.
For example for : 12 3 61 23 51 2 the greedily decreasing sequence is built like this:
12 -> 12 3 -> we ignore 61 because it's worse than 3 -> we ignore 23 because it's worse than 3 -> we ignore 51 because it's worse than 3 -> 12 3 2.
So the answer would contain on the left side 12 3 or 2.
Now on a random case this has O(log N) length so you can binary search on it for each element as the right part of the answer and you would get O(N log log N) which is good, and if you apply the same logic on the right part of the string on a random case you could get O(log^2 N + N(from the reading)) which is O(N). But we can do O(N) on a non-random case too.
Suppose we have this decreasing sequence. We start from the right of the string and do the following while we can pair the last of the decreasing sequence with the current number
1) If we found a better solution by taking the last of the decreasing sequence and the current number than we update the answer
2) Even if we updated the answer or not we pop the last element of the decreasing sequence because we are it's perfect match (any other match would be to the left and would give an answer with smaller j - i)
3) Repeat while we can pair these 2
Example Code:
#include <iostream>
#include <vector>
using namespace std;
int main() {
int N; cin >> N;
vector<int> A(N + 1);
for (int i = 1; i <= N; ++i)
cin >> A[i];
// let's solve the problem
vector<int> decreasing;
pair<int, int> answer;
// build the decreasing sequence
decreasing.push_back(1);
for (int i = 1; i <= N; ++i)
if (A[i] < A[decreasing.back()])
decreasing.push_back(i); // we work with indexes because we might have equal values
for (int i = N; i > 0; --i) {
while (decreasing.size() and A[decreasing.back()] < A[i]) { // while we can pair these 2
pair<int, int> current_pair(decreasing.back(), i);
if (current_pair.second - current_pair.first > answer.second - answer.first)
answer = current_pair;
decreasing.pop_back();
}
}
cout << "Best pair found: (" << answer.first << ", " << answer.second << ") with values (" << A[answer.first] << ", " << A[answer.second] << ")\n";
}
Later Edit:
I see you gave an example: I indexed from 1 to make it clearer and I print (i, j) instead of (j, i). You can alter it as you see fit.
We can avoid checking the whole array by starting from the maximum difference of j-i and comparing arr[j]>arr[i] for all the possible combinations j and i for that particular maximum difference
Whenever we get a combination of (j,i) with arr[j]>arr[i] we can exit the loop
Example : In an array of {2,3,4,5,8,1}
first code will check for maximum difference 5(5-0) i.e (arr[0],arr[5]), if arr[5]>arr[0] function will exit else will take combinations of max diff 4 (5,1) and (4,0) i.e arr[5],arr[1] and arr[4],arr[0]
int maxIndexDiff(int arr[], int n)
{
int maxDiff = n-1;
int i, j;
while (maxDiff>0)
{
j=n-1;
while(j>=maxDiff)
{
i=j - maxDiff;
if(arr[j]>arr[i])
{
return maxDiff;
}
j=j-1;
}
maxDiff=maxDiff-1;
}
return -1;
}`
https://ide.geeksforgeeks.org/cjCW3wXjcj
Here is a very simple O(n) Python implementation of the merged down-sequence idea. The implementation works even in the case of duplicate values:
downs = [0]
for i in range(N):
if ar[i] < ar[downs[-1]]:
downs.append(i)
best = 0
i, j = len(downs)-1, N-1
while i >= 0:
if ar[downs[i]] <= ar[j]:
best = max(best, j-downs[i])
i -= 1
else:
j -= 1
print best
To solve this problem, we need to get two optimum indexes of arr[]: left index i and right index j. For an element arr[i], we do not need to consider arr[i] for left index if there is an element smaller than arr[i] on left side of arr[i]. Similarly, if there is a greater element on right side of arr[j] then we do not need to consider this j for right index. So we construct two auxiliary arrays LMin[] and RMax[] such that LMin[i] holds the smallest element on left side of arr[i] including arr[i], and RMax[j] holds the greatest element on right side of arr[j] including arr[j]. After constructing these two auxiliary arrays, we traverse both of these arrays from left to right. While traversing LMin[] and RMa[] if we see that LMin[i] is greater than RMax[j], then we must move ahead in LMin[] (or do i++) because all elements on left of LMin[i] are greater than or equal to LMin[i]. Otherwise we must move ahead in RMax[j] to look for a greater j – i value. Here is the c code running in O(n) time:
#include <stdio.h>
#include <stdlib.h>
/* Utility Functions to get max and minimum of two integers */
int max(int x, int y)
{
return x > y? x : y;
}
int min(int x, int y)
{
return x < y? x : y;
}
/* For a given array arr[], returns the maximum j – i such that
arr[j] > arr[i] */
int maxIndexDiff(int arr[], int n)
{
int maxDiff;
int i, j;
int *LMin = (int *)malloc(sizeof(int)*n);
int *RMax = (int *)malloc(sizeof(int)*n);
/* Construct LMin[] such that LMin[i] stores the minimum value
from (arr[0], arr[1], ... arr[i]) */
LMin[0] = arr[0];
for (i = 1; i < n; ++i)
LMin[i] = min(arr[i], LMin[i-1]);
/* Construct RMax[] such that RMax[j] stores the maximum value
from (arr[j], arr[j+1], ..arr[n-1]) */
RMax[n-1] = arr[n-1];
for (j = n-2; j >= 0; --j)
RMax[j] = max(arr[j], RMax[j+1]);
/* Traverse both arrays from left to right to find optimum j - i
This process is similar to merge() of MergeSort */
i = 0, j = 0, maxDiff = -1;
while (j < n && i < n)
{
if (LMin[i] < RMax[j])
{
maxDiff = max(maxDiff, j-i);
j = j + 1;
}
else
i = i+1;
}
return maxDiff;
}
/* Driver program to test above functions */
int main()
{
int arr[] = {1, 2, 3, 4, 5, 6};
int n = sizeof(arr)/sizeof(arr[0]);
int maxDiff = maxIndexDiff(arr, n);
printf("\n %d", maxDiff);
getchar();
return 0;
}
Simplified version of Subhasis Das answer using auxiliary arrays.
def maxdistance(nums):
n = len(nums)
minima ,maxima = [None]*n, [None]*n
minima[0],maxima[n-1] = nums[0],nums[n-1]
for i in range(1,n):
minima[i] = min(nums[i],minima[i-1])
for i in range(n-2,-1,-1):
maxima[i]= max(nums[i],maxima[i+1])
i,j,maxdist = 0,0,-1
while(i<n and j<n):
if minima[i] <maxima[j]:
maxdist = max(j-i,maxdist)
j = j+1
else:
i += 1
print maxdist
I can think of improvement over O(n^2), but need to verify if this is O(n) in worse case or not.
Create a variable BestSoln=0; and traverse the array for first element
and store the best solution for first element i.e bestSoln=k;.
Now for 2nd element consider only elements which are k distances away
from the second element.
If BestSoln in this case is better than first iteration then replace
it otherwise let it be like that. Keep iterating for other elements.
It can be improved further if we store max element for each subarray starting from i to end.
This can be done in O(n) by traversing the array from end.
If a particular element is more than it's local max then there is no need to do evaluation for this element.
Input:
{9, 2, 3, 4, 5, 6, 7, 8, 18, 0}
create local max array for this array:
[18,18,18,18,18,18,18,0,0] O(n).
Now, traverse the array for 9 ,here best solution will be i=0,j=8.
Now for second element or after it, we don't need to evaluate. and best solution is i=0,j=8.
But suppose array is Input:
{19, 2, 3, 4, 5, 6, 7, 8, 18, 0,4}
Local max array [18,18,18,18,18,18,18,0,0] then in first iteration we don't need to evaluate as local max is less than current elem.
Now for second iteration best solution is, i=1,j=10. Now for other elements we don't need to consider evaluation as they can't give best solution.
Let me know your view your use case to which my solution is not applicable.
This is a very simple solution for O(2n) of speed and additional ~O(2n) of space (in addition to the input array). The following implementation is in C:
int findMaxDiff(int array[], int size) {
int index = 0;
int maxima[size];
int indexes[size];
while (index < size) {
int max = array[index];
int i;
for (i = index; i < size; i++) {
if (array[i] > max) {
max = array[i];
indexes[index] = i;
}
}
maxima[index] = max;
index++;
}
int j;
int result;
for (j = 0; j < size; j++) {
int max2 = 0;
if (maxima[j] - array[j] > max2) {
max2 = maxima[j] - array[j];
result = indexes[j];
}
}
return result;
}
The first loop scan the array once, finding for each element the maximum of the remaining elements to its right. We store also the relative index in a separate array.
The second loops finds the maximum between each element and the correspondent right-hand-side maximum, and returns the right index.
My Solution with in O(log n) (Please correct me here if I am wrong in calculating this complexity)time ...
Idea is to insert into a BST and then search for node and if the node has a right child then traverse through the right sub tree to calculate the node with maximum index..
import java.util.*;
import java.lang.*;
import java.io.*;
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
public static void main (String[] args) throws IOException{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t1 = Integer.parseInt(br.readLine());
for(int j=0;j<t1;j++){
int size = Integer.parseInt(br.readLine());
String input = br.readLine();
String[] t = input.split(" ");
Node root = new Node(Integer.parseInt(t[0]),0);
for(int i=1;i<size;i++){
Node addNode = new Node(Integer.parseInt(t[i]),i);
insertIntoBST(root,addNode);
}
for(String s: t){
Node nd = findNode(root,Integer.parseInt(s));
if(nd.right != null){
int i = nd.index;
int j1 = calculate(nd.right);
mVal = max(mVal,j1-i);
}
}
System.out.println(mVal);
mVal=0;
}
}
static int mVal =0;
public static int calculate (Node root){
if(root==null){
return -1;
}
int i = max(calculate(root.left),calculate(root.right));
return max(root.index,i);
}
public static Node findNode(Node root,int n){
if(root==null){
return null;
}
if(root.value == n){
return root;
}
Node result = findNode(root.left,n);
if(result ==null){
result = findNode(root.right,n);
}
return result;
}
public static int max(int a , int b){
return a<b?b:a;
}
public static class Node{
Node left;
Node right;
int value;
int index;
public Node(int value,int index){
this.value = value;
this.index = index;
}
}
public static void insertIntoBST(Node root, Node addNode){
if(root.value< addNode.value){
if(root.right!=null){
insertIntoBST(root.right,addNode);
}else{
root.right = addNode;
}
}
if(root.value>=addNode.value){
if(root.left!=null){
insertIntoBST(root.left,addNode);
}else{
root.left =addNode;
}
}
}
}
A simplified algorithm from Subhasis Das's answer:
# assume list is not empty
max_dist = 0
acceptable_min = (0, arr[0])
acceptable_max = (0, arr[0])
min = (0, arr[0])
for i in range(len(arr)):
if arr[i] < min[1]:
min = (i, arr[i])
elif arr[i] - min[1] > max_dist:
max_dist = arr[i] - min[1]
acceptable_min = min
acceptable_max = (i, arr[i])
# acceptable_min[0] is the i
# acceptable_max[0] is the j
# max_dist is the max difference
Below is a C++ solution for the condition a[i] <= a[j]. It needs a slight modification to handle the case a[i] < a[j].
template<typename T>
std::size_t max_dist_sorted_pair(const std::vector<T>& seq)
{
const auto n = seq.size();
const auto less = [&seq](std::size_t i, std::size_t j)
{ return seq[i] < seq[j]; };
// max_right[i] is the position of the rightmost
// largest element in the suffix seq[i..]
std::vector<std::size_t> max_right(n);
max_right.back() = n - 1;
for (auto i = n - 1; i > 0; --i)
max_right[i - 1] = std::max(max_right[i], i - 1, less);
std::size_t max_dist = 0;
for (std::size_t i = 0, j = 0; i < n; ++i)
while (!less(max_right[j], i))
{
j = max_right[j];
max_dist = std::max(max_dist, j - i);
if (++j == n)
return max_dist;
}
return max_dist;
}
Please review this solution and cases where it might fail:
def maxIndexDiff(arr, n):
j = n-1
for i in range(0,n):
if j > i:
if arr[j] >= arr[i]:
return j-i
elif arr[j-1] >= arr[i]:
return (j-1) - i
elif arr[j] >= arr[i+1]:
return j - (i+1)
j -= 1
return -1
int maxIndexDiff(int arr[], int n)
{
// Your code here
vector<int> rightMax(n);
rightMax[n-1] = arr[n-1];
for(int i =n-2;i>=0;i--){
rightMax[i] = max(rightMax[i+1],arr[i]);
}
int i = 0,j=0,maxDis = 0;
while(i<n &&j<n){
if(rightMax[j]>=arr[i]){
maxDis = max(maxDis,j-i);
j++;
} else
i++;
}
return maxDis;
}
There is concept of keeping leftMin and rightMax but leftMin is not really required and leftMin will do the work anyways.
We are choosing rightMax and traversing from start till we get a smaller value than that!
Create Arraylist of pairs where is key is array element and value is the index. Sort this arraylist of pairs. Traverse this arraylist of pairs to get the maximum gap between(maxj-i). Also keep a track of maxj and update when new maxj is found. Please find my java solution which takes O(nlogn) time complexity and O(n) space complexity.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
class MaxDistanceSolution {
private class Pair implements Comparable<Pair> {
int key;
int value;
public int getKey() {
return key;
}
public int getValue() {
return value;
}
Pair(int key, int value) {
this.key = key;
this.value = value;
}
#Override
public int compareTo(Pair o) {
return this.getKey() - o.getKey();
}
}
public int maximumGap(final ArrayList<Integer> A) {
int n = A.size();
ArrayList<Pair> B = new ArrayList<>();
for (int i = 0 ; i < n; i++)
B.add(new Pair(A.get(i), i));
Collections.sort(B);
int maxJ = B.get(n-1).getValue();
int gaps = 0;
for (int i = n - 2; i >= 0; i--) {
gaps = Math.max(gaps, maxJ - B.get(i).getValue());
maxJ = Math.max(maxJ, B.get(i).getValue());
}
return gaps;
}
}
public class MaxDistance {
public static void main(String[] args) {
MaxDistanceSolution sol = new MaxDistanceSolution();
ArrayList<Integer> A = new ArrayList<>(Arrays.asList(3, 5, 4, 2));
int gaps = sol.maximumGap(A);
System.out.println(gaps);
}
}
I have solved this question here.
https://github.com/nagendra547/coding-practice/blob/master/src/arrays/FindMaxIndexDifference.java
Putting code here too. Thanks.
private static int findMaxIndexDifferenceOptimal(int[] a) {
int n = a.length;
// array containing minimums
int A[] = new int[n];
A[0] = a[0];
for (int i = 1; i < n; i++) {
A[i] = Math.min(a[i], A[i - 1]);
}
// array containing maximums
int B[] = new int[n];
B[n - 1] = a[n - 1];
for (int j = n - 2; j >= 0; j--) {
B[j] = Math.max(a[j], B[j + 1]);
}
int i = 0, maxDiff = -1;
int j = 0;
while (i < n && j < n) {
if (B[j] > A[i]) {
maxDiff = Math.max(j - i, maxDiff);
j++;
} else {
i++;
}
}
return maxDiff;
}
I recently went through an interview and was asked this question. Let me explain the question properly:
Given a number M (N-digit integer) and K number of swap operations(a swap
operation can swap 2 digits), devise an algorithm to get the maximum
possible integer?
Examples:
M = 132 K = 1 output = 312
M = 132 K = 2 output = 321
M = 7899 k = 2 output = 9987
My solution ( algorithm in pseudo-code). I used a max-heap to get the maximum digit out of N-digits in each of the K-operations and then suitably swapping it.
for(int i = 0; i<K; i++)
{
int max_digit_currently = GetMaxFromHeap();
// The above function GetMaxFromHeap() pops out the maximum currently and deletes it from heap
int index_to_swap_with = GetRightMostOccurenceOfTheDigitObtainedAbove();
// This returns me the index of the digit obtained in the previous function
// .e.g If I have 436659 and K=2 given,
// then after K=1 I'll have 936654 and after K=2, I should have 966354 and not 963654.
// Now, the swap part comes. Here the gotcha is, say with the same above example, I have K=3.
// If I do GetMaxFromHeap() I'll get 6 when K=3, but I should not swap it,
// rather I should continue for next iteration and
// get GetMaxFromHeap() to give me 5 and then get 966534 from 966354.
if (Value_at_index_to_swap == max_digit_currently)
continue;
else
DoSwap();
}
Time complexity: O(K*( N + log_2(N) ))
// K-times [log_2(N) for popping out number from heap & N to get the rightmost index to swap with]
The above strategy fails in this example:
M = 8799 and K = 2
Following my strategy, I'll get M = 9798 after K=1 and M = 9978 after K=2. However, the maximum I can get is M = 9987 after K=2.
What did I miss?
Also suggest other ways to solve the problem & ways to optimize my solution.
I think the missing part is that, after you've performed the K swaps as in the algorithm described by the OP, you're left with some numbers that you can swap between themselves. For example, for the number 87949, after the initial algorithm we would get 99748. However, after that we can swap 7 and 8 "for free", i.e. not consuming any of the K swaps. This would mean "I'd rather not swap the 7 with the second 9 but with the first".
So, to get the max number, one would perform the algorithm described by the OP and remember the numbers which were moved to the right, and the positions to which they were moved. Then, sort these numbers in decreasing order and put them in the positions from left to right.
This is something like a separation of the algorithm in two phases - in the first one, you choose which numbers should go in the front to maximize the first K positions. Then you determine the order in which you would have swapped them with the numbers whose positions they took, so that the rest of the number is maximized as well.
Not all the details are clear, and I'm not 100% sure it handles all cases correctly, so if anyone can break it - go ahead.
This is a recursive function, which sorts the possible swap values for each (current-max) digit:
function swap2max(string, K) {
// the recursion end:
if (string.length==0 || K==0)
return string
m = getMaxDigit(string)
// an array of indices of the maxdigits to swap in the string
indices = []
// a counter for the length of that array, to determine how many chars
// from the front will be swapped
len = 0
// an array of digits to be swapped
front = []
// and the index of the last of those:
right = 0
// get those indices, in a loop with 2 conditions:
// * just run backwards through the string, until we meet the swapped range
// * no more swaps than left (K)
for (i=string.length; i-->right && len<K;)
if (m == string[i])
// omit digits that are already in the right place
while (right<=i && string[right] == m)
right++
// and when they need to be swapped
if (i>=right)
front.push(string[right++])
indices.push(i)
len++
// sort the digits to swap with
front.sort()
// and swap them
for (i=0; i<len; i++)
string.setCharAt(indices[i], front[i])
// the first len digits are the max ones
// the rest the result of calling the function on the rest of the string
return m.repeat(right) + swap2max(string.substr(right), K-len)
}
This is all pseudocode, but converts fairly easy to other languages. This solution is nonrecursive and operates in linear worst case and average case time.
You are provided with the following functions:
function k_swap(n, k1, k2):
temp = n[k1]
n[k1] = n[k2]
n[k2] = temp
int : operator[k]
// gets or sets the kth digit of an integer
property int : magnitude
// the number of digits in an integer
You could do something like the following:
int input = [some integer] // input value
int digitcounts[10] = {0, ...} // all zeroes
int digitpositions[10] = {0, ...) // all zeroes
bool filled[input.magnitude] = {false, ...) // all falses
for d = input[i = 0 => input.magnitude]:
digitcounts[d]++ // count number of occurrences of each digit
digitpositions[0] = 0;
for i = 1 => input.magnitude:
digitpositions[i] = digitpositions[i - 1] + digitcounts[i - 1] // output positions
for i = 0 => input.magnitude:
digit = input[i]
if filled[i] == true:
continue
k_swap(input, i, digitpositions[digit])
filled[digitpositions[digit]] = true
digitpositions[digit]++
I'll walk through it with the number input = 724886771
computed digitcounts:
{0, 1, 1, 0, 1, 0, 1, 3, 2, 0}
computed digitpositions:
{0, 0, 1, 2, 2, 3, 3, 4, 7, 9}
swap steps:
swap 0 with 0: 724886771, mark 0 visited
swap 1 with 4: 724876781, mark 4 visited
swap 2 with 5: 724778881, mark 5 visited
swap 3 with 3: 724778881, mark 3 visited
skip 4 (already visited)
skip 5 (already visited)
swap 6 with 2: 728776481, mark 2 visited
swap 7 with 1: 788776421, mark 1 visited
swap 8 with 6: 887776421, mark 6 visited
output number: 887776421
Edit:
This doesn't address the question correctly. If I have time later, I'll fix it but I don't right now.
How I would do it (in pseudo-c -- nothing fancy), assuming a fantasy integer array is passed where each element represents one decimal digit:
int[] sortToMaxInt(int[] M, int K) {
for (int i = 0; K > 0 && i < M.size() - 1; i++) {
if (swapDec(M, i)) K--;
}
return M;
}
bool swapDec(int[]& M, int i) {
/* no need to try and swap the value 9 as it is the
* highest possible value anyway. */
if (M[i] == 9) return false;
int max_dec = 0;
int max_idx = 0;
for (int j = i+1; j < M.size(); j++) {
if (M[j] >= max_dec) {
max_idx = j;
max_dec = M[j];
}
}
if (max_dec > M[i]) {
M.swapElements(i, max_idx);
return true;
}
return false;
}
From the top of my head so if anyone spots some fatal flaw please let me know.
Edit: based on the other answers posted here, I probably grossly misunderstood the problem. Anyone care to elaborate?
You start with max-number(M, N, 1, K).
max-number(M, N, pos, k)
{
if k == 0
return M
max-digit = 0
for i = pos to N
if M[i] > max-digit
max-digit = M[i]
if M[pos] == max-digit
return max-number(M, N, pos + 1, k)
for i = (pos + 1) to N
maxs.add(M)
if M[i] == max-digit
M2 = new M
swap(M2, i, pos)
maxs.add(max-number(M2, N, pos + 1, k - 1))
return maxs.max()
}
Here's my approach (It's not fool-proof, but covers the basic cases). First we'll need a function that extracts each DIGIT of an INT into a container:
std::shared_ptr<std::deque<int>> getDigitsOfInt(const int N)
{
int number(N);
std::shared_ptr<std::deque<int>> digitsQueue(new std::deque<int>());
while (number != 0)
{
digitsQueue->push_front(number % 10);
number /= 10;
}
return digitsQueue;
}
You obviously want to create the inverse of this, so convert such a container back to an INT:
const int getIntOfDigits(const std::shared_ptr<std::deque<int>>& digitsQueue)
{
int number(0);
for (std::deque<int>::size_type i = 0, iMAX = digitsQueue->size(); i < iMAX; ++i)
{
number = number * 10 + digitsQueue->at(i);
}
return number;
}
You also will need to find the MAX_DIGIT. It would be great to use std::max_element as it returns an iterator to the maximum element of a container, but if there are more you want the last of them. So let's implement our own max algorithm:
int getLastMaxDigitOfN(const std::shared_ptr<std::deque<int>>& digitsQueue, int startPosition)
{
assert(!digitsQueue->empty() && digitsQueue->size() > startPosition);
int maxDigitPosition(0);
int maxDigit(digitsQueue->at(startPosition));
for (std::deque<int>::size_type i = startPosition, iMAX = digitsQueue->size(); i < iMAX; ++i)
{
const int currentDigit(digitsQueue->at(i));
if (maxDigit <= currentDigit)
{
maxDigit = currentDigit;
maxDigitPosition = i;
}
}
return maxDigitPosition;
}
From here on its pretty straight what you have to do, put the right-most (last) MAX DIGITS to their places until you can swap:
const int solution(const int N, const int K)
{
std::shared_ptr<std::deque<int>> digitsOfN = getDigitsOfInt(N);
int pos(0);
int RemainingSwaps(K);
while (RemainingSwaps)
{
int lastHDPosition = getLastMaxDigitOfN(digitsOfN, pos);
if (lastHDPosition != pos)
{
std::swap<int>(digitsOfN->at(lastHDPosition), digitsOfN->at(pos));
++pos;
--RemainingSwaps;
}
}
return getIntOfDigits(digitsOfN);
}
There are unhandled corner-cases but I'll leave that up to you.
I assumed K = 2, but you can change the value!
Java code
public class Solution {
public static void main (String args[]) {
Solution d = new Solution();
System.out.println(d.solve(1234));
System.out.println(d.solve(9812));
System.out.println(d.solve(9876));
}
public int solve(int number) {
int[] array = intToArray(number);
int[] result = solve(array, array.length-1, 2);
return arrayToInt(result);
}
private int arrayToInt(int[] array) {
String s = "";
for (int i = array.length-1 ;i >= 0; i--) {
s = s + array[i]+"";
}
return Integer.parseInt(s);
}
private int[] intToArray(int number){
String s = number+"";
int[] result = new int[s.length()];
for(int i = 0 ;i < s.length() ;i++) {
result[s.length()-1-i] = Integer.parseInt(s.charAt(i)+"");
}
return result;
}
private int[] solve(int[] array, int endIndex, int num) {
if (endIndex == 0)
return array;
int size = num ;
int firstIndex = endIndex - size;
if (firstIndex < 0)
firstIndex = 0;
int biggest = findBiggestIndex(array, endIndex, firstIndex);
if (biggest!= endIndex) {
if (endIndex-biggest==num) {
while(num!=0) {
int temp = array[biggest];
array[biggest] = array[biggest+1];
array[biggest+1] = temp;
biggest++;
num--;
}
return array;
}else{
int n = endIndex-biggest;
for (int i = 0 ;i < n;i++) {
int temp = array[biggest];
array[biggest] = array[biggest+1];
array[biggest+1] = temp;
biggest++;
}
return solve(array, --biggest, firstIndex);
}
}else{
return solve(array, --endIndex, num);
}
}
private int findBiggestIndex(int[] array, int endIndex, int firstIndex) {
int result = firstIndex;
int max = array[firstIndex];
for (int i = firstIndex; i <= endIndex; i++){
if (array[i] > max){
max = array[i];
result = i;
}
}
return result;
}
}
I read through all subset sum topics and still have issues with implementing the algorithm for the following problem.
Given the array A of N integers (N<=20) where
a[i]<=20
values do not have to be unique
and an integer K (K<=20).
Rules:
Array items equal to K are "covered" with K.
If sum of two or more array numbers is equal to K, these numbers are also covered.
Each number in the array can be covered only once.
Example:
N=6, integers: 1, 1, 2, 3, 4, 5
K=4
Possible coverages:
coverage
4 is covered.
1, 1, 2 are covered as 1+1+2=4.
coverage
4 is covered.
1, 3 are covered as 1+3=4.
K=5
Possible coverages:
coverage
5 is covered.
1,1,3 are covered as 1+1+3=5.
coverage
5 is covered.
1,4 are covered as 1+4=5.
2,3 are covered as 2+3=5.
Goal:
For given array A and integer K, find all possible "coverages". I need all coverages, not only one which covers most of the array items.
I have tried with two approaches:
Brut force algorithm.
Checking all possible subsets of all possible sizes works, but takes too much time even for only 10 numbers. I need it to finish in no more than 500ms.
First, I sorted the array in descending order. Then for each possible number of sub-sums I create "slots". I loop through the array and put numbers in the slots following the rules like:
Put number in the slot if its sum becomes equal to K.
Put number in the slot having the least sum of all slots.
Put number in the slot which gives the closet sum to K of all slots.
Well, the second approach works and works fast. But I found scenarios where some coverages are not found.
I would appreciate if somebody offered idea for solving this problem.
I hope I explained the problem well.
Thanks.
I don't have ready answer for that, but I recommend to take a look on 'Bin packing problem' it could be usefull here.
The main problem is to find all possible sums giving number K. So try this:
Collection All_Possible_Sums_GivingK;
find_All_Sums_Equal_To_K(Integer K, Array A)
{
/* this function after finding result
add it to global Collection AllPossibleSumsGivingK; */
find_All_Elements_Equal_To_K(Integer K, Array A);
Array B = Remove_Elements_Geater_Or_Equal_To_K(Integer K, Array A);
for all a in A {
find_All_Sums_Equal_To_K(Integer K-a, Array B-a)
}
}
I modified this from an earlier answer I gave to a different subset sum variant: https://stackoverflow.com/a/10612601/120169
I am running it here on the K=8 case with the above numbers, where we reuse 1 in two different places for one of the two "coverages". Let me know how it works for you.
public class TurboAdder2 {
// Problem inputs
// The unique values
private static final int[] data = new int[] { 1, 2, 3, 4, 5 };
// counts[i] = the number of copies of i
private static final int[] counts = new int[] { 2, 1, 1, 1, 1 };
// The sum we want to achieve
private static int target = 8;
private static class Node {
public final int index;
public final int count;
public final Node prevInList;
public final int prevSum;
public Node(int index, int count, Node prevInList, int prevSum) {
this.index = index;
this.count = count;
this.prevInList = prevInList;
this.prevSum = prevSum;
}
}
private static Node sums[] = new Node[target+1];
// Only for use by printString and isSolvable.
private static int forbiddenValues[] = new int[data.length];
private static boolean isSolvable(Node n) {
if (n == null) {
return true;
} else {
while (n != null) {
int idx = n.index;
// We prevent recursion on a value already seen.
// Don't use any indexes smaller than lastIdx
if (forbiddenValues[idx] + n.count <= counts[idx]) {
// Verify that none of the bigger indexes are set
forbiddenValues[idx] += n.count;
boolean ret = isSolvable(sums[n.prevSum]);
forbiddenValues[idx] -= n.count;
if (ret) {
return true;
}
}
n = n.prevInList;
}
return false;
}
}
public static void printString(String prev, Node n, int firstIdx, int lastIdx) {
if (n == null) {
printString(prev +" |", sums[target], -1, firstIdx);
} else {
if (firstIdx == -1 && !isSolvable(sums[target])) {
int lidx = prev.lastIndexOf("|");
if (lidx != -1) {
System.out.println(prev.substring(0, lidx));
}
}
else {
while (n != null) {
int idx = n.index;
// We prevent recursion on a value already seen.
// Don't use any indexes larger than lastIdx
if (forbiddenValues[idx] + n.count <= counts[idx] && (lastIdx < 0 || idx < lastIdx)) {
// Verify that none of the bigger indexes are set
forbiddenValues[idx] += n.count;
printString((prev == null ? "" : (prev + (prev.charAt(prev.length()-1) == '|' ? " " : " + ")))+data[idx]+"*"+n.count, sums[n.prevSum], (firstIdx == -1 ? idx : firstIdx), idx);
forbiddenValues[idx] -= n.count;
}
n = n.prevInList;
}
}
}
}
public static void main(String[] args) {
for (int i = 0; i < data.length; i++) {
int value = data[i];
for (int count = 1, sum = value; count <= counts[i] && sum <= target; count++, sum += value) {
for (int newsum = sum+1; newsum <= target; newsum++) {
if (sums[newsum - sum] != null) {
sums[newsum] = new Node(i, count, sums[newsum], newsum - sum);
}
}
}
for (int count = 1, sum = value; count <= counts[i] && sum <= target; count++, sum += value) {
sums[sum] = new Node(i, count, sums[sum], 0);
}
}
printString(null, sums[target], -1, -1);
}
}