I haven't been able to come up with a bullet proof answer to this question. My solution fails few cases. I would appreciate some insights.
Question:
Given two strings A and B, return the number of times A needs to be stated such that it contains string B?
Example #1:
String A : abcd
String B : cdabcdab
Should return 3 because:
abcdabcdabcd ( A repeated 3 times)
cdabcdab ( B is contained in now)
Example #2:
String A = abcd
String B = d
should return 1 because B is already a substring of A.
Example #3:
String A = abcd
String B = cda
Should return 2 because:
abcdabcd
cda
Example #4:
String A = abcd
String B = cdb
Should return -1, it doesn't matter how many times we state A, there is no way we can produce B.
Few insights I have noticed:
Order of characters matter
A must contain at least all the
characters in B
Neither A or B needs to be a substring of the
other.
There must be an overlap between the end of one string and
the beginning of the other.
If |B| > 2|A| - 2 and B occurs in A^n, then A occurs in B. Count and remove all complete instances of A in B, and then the solution is this count plus the solution to the same problem with A's removed from B.
Otherwise, it is guaranteed that if B appears in A^n, it appears in A^3. Construct A^3 and find the first occurrence of B in it. Find and remove any complete instances of A appearing after the end of B's appearance in A^3. Return 3 minus the number of removed instances.
Examples:
f(abcd, cdabcdab)
|cdabcdab| > 2|abcd| - 2 since 8 > 2*4 - 2
^^^^
first instance of A in B; no more, so return 1 + f(cdab, abcd) = 3
f(cdab, abcd)
|cdab| < 2|abcd| - 2 since 4 < 2*4 - 2
abcdabcdabcd
^^^^
first instance of B in A; one instance of A after B, so return 3 - 1 = 2.
f(d, abcd)
|d| < 2|abcd| - 2, since 1 < 2*4 - 2
abcdabcdabcd
^
first instance of B in A; two instances of A after B, so return 3 - 2 = 1.
f(cda, abcd)
|cda| = 2|abcd| - 2 since 3 = 2*4 - 2
abcdabcdabcd
^^^
first instance of B in A; one instance of A after B, so return 3 - 1 = 2.
f(cdb, abcd)
|cbd| = 2|abcd| - 2 since 3 = 2*3 - 2
abcdabcdabcd
^ no instances of B in A; return -1.
Some minor optimizations include:
if |B| = 0, return 0.
if |B| = 1, use A^1 instead of A^3.
if |B| < |A| + 2, use A^2 instead of A^3.
One way to do it as like the code segment below. I noticed that no matter how many times we duplicate string A, this number (of times) can't be greater than length of string B. I hope this helps. Please note my answer runs in O(N^2) time. Not Ideal but any brute force solution should give you a good start towards the optimum/final solution.
string A = "abcd";
string B = "cda";
int i = 1;
string S = A;
while (i < B.Length)
{
S = S + A;
i++;
if(S.Contains(B))
break;
}
if(i==B.Length-1 && !S.Contains(B))
Console.WriteLine(-1); //not found
Console.WriteLine(i); //the solution
#include <iostream>
#include <string>
using namespace std;
int main()
{
string a,b,s="";
cin>>a>>b;int count=0;
size_t f = a.find(b);
if(f==string::npos)
{
for(int i=0;i<b.length() && s.find(b)==string::npos;++i)
{
s.append(a);
count++;
}
}
else
{
cout<<1<<endl;
return 0;
}
if(s.find(b)!=string::npos)
cout<<count;
else
cout<<0<<endl;
return 0;
}
If A is longer than B then return 1 if B is in A.
if A is same length as B and they are equal return 1.
Look for the location in which B contains A, with a wrap around.
So A is abc and B is bca you will find that A is in B starting at [2]. Then start covering B with A starting with that location and count how many times you had to repeat A. Note that if covering fails, you need to keep searching for other possible places where A is in B.
it is guaranteed that if B appears in A^n, it appears in A^3.
So writing simple Java Code :
import java.io.*;
public class StringDemo {
public static void print(String x){
System.out.println(x);
}
public static void main(String args[]) {
String A = "abcd";
int alen = A.length();
String B = "cda";
int blen = B.length();
String C = A+A+A;
int op = -1;
if (C.indexOf(B) > -1 ){
op = 3;
C = C.substring(0,alen*2);
if (C.indexOf(B) > -1){
op = 2;
C = C.substring(0,alen);
if (C.indexOf(B) > -1){
op = 1;
}
}
}
print(Integer.toString(op));
}
}
There is a similar question I solved few days ago.
The Question :
Given two strings A and B, find the minimum number of times A has to be repeated such that B is a substring of it. If no such solution, return -1.
For example, with A = "abcd" and B = "abcdabcd".
Return 3, because by repeating A three times (“abcdabcdabcd”), B is a substring of it; and B is not a substring of A repeated two times ("abcdabcd").
One probable solution from my side can be this:
public class test1 {
public static void main(String[] args) {
String a = " abcd";
String b = "abcdabcd";
System.out.println(fix(a,b));
}
public static int fix(String a,String b) {
StringBuffer sbr = new StringBuffer(a);
int c = 1 ;
//for( ; sbr.length() < b.length() ; c++ ) {sbr.append(a) ; }
while(sbr.length() < b.length() ) {
sbr.append(a);
c++ ;
}
String t = sbr.toString();
// if str1 not contains then we can concatenate and we must increase the count
if(!t.contains(b)) {
t += a ;
c++ ;
}
if(t.contains(b)) {
c++ ;
}
return c ;
}
}
The output will be 3 .abcdabcdabcd => 3 times abcd then abcdabcd will be a substring of it. That's why answer 3 is correct. If str1 has str2 the we increment the count by 1.
My solution is naive, but I think it works fine. If anyone found a flaw in this, please let me know.
private static int countRepeatOfString(StringBuffer concatenate, String a, String b) {
if (concatenate.length() == 0 || b.length() == 0) {
return -1;
}
int maxConcatenateCount;
/* For cases like:
String A - abcd (length=4) Longest possible would be:
String B - cdabcdab (length=8) abcdabcdabcd
Let r = the ratio of String B length to String A length
r + 2 is for taking care of case:
String A - abc
String B - c(abc)a
*/
if (a.length() <= b.length()) {
maxConcatenateCount = b.length() / a.length() + 2;
return countOccurrence(maxConcatenateCount, concatenate, a, b);
} else {
return countOccurrence(2, concatenate, a, b);
}
}
private static int countOccurrence(int maxConcatenateCount, StringBuffer concatenate, String a, String b) {
boolean found = false;
int currentConcatenateCount = 1;
int repeatCount = 1;
while (currentConcatenateCount <= maxConcatenateCount) {
int index = concatenate.indexOf(b, 0);
if (index != -1) {
found = true;
break;
}
concatenate.append(a);
currentConcatenateCount++;
repeatCount++;
}
if (found) {
return repeatCount;
} else {
return -1;
}
}
Taking the solution from #Patrick87
Here is the code:
public class ATimesToContainB {
public static void main(String args[]) {
System.out.println();
String a = "abcd";
String b = "cdabcdabcdabcdab";
System.out.println("Brute Force Multiply A :" + a + " n= " + atimesbBruteForce(a, b) + " to contain B " + b);
System.out.println("Optimized Multiply A :" + a + " n= " + atimesb(a, b) + " to contain B " + b);
System.out.println();
a = "abcd";
b = "cdabcdabcdabcdabab";
System.out.println("Brute Force Multiply A :" + a + " n= " + atimesbBruteForce(a, b) + " to contain B " + b);
System.out.println("Optimized Multiply A :" + a + " n= " + atimesb(a, b) + " to contain B " + b);
System.out.println();
a = "abcd";
b = "cdabcdab";
System.out.println("Brute Force Multiply A :" + a + " n= " + atimesbBruteForce(a, b) + " to contain B " + b);
System.out.println("Optimized Multiply A :" + a + " n= " + atimesb(a, b) + " to contain B " + b);
System.out.println();
a = "abcd";
b = "d";
System.out.println("Brute Force Multiply A :" + a + " n= " + atimesbBruteForce(a, b) + " to contain B " + b);
System.out.println("Optimized Multiply A :" + a + " n= " + atimesb(a, b) + " to contain B " + b);
System.out.println();
a = "abcd";
b = "cda";
System.out.println("Brute Force Multiply A :" + a + " n= " + atimesbBruteForce(a, b) + " to contain B " + b);
System.out.println("Optimized Multiply A :" + a + " n= " + atimesb(a, b) + " to contain B " + b);
System.out.println();
a = "abcd";
b = "cdb";
System.out.println("Brute Force Multiply A :" + a + " n= " + atimesbBruteForce(a, b) + " to contain B " + b);
System.out.println("Optimized Multiply A :" + a + " n= " + atimesb(a, b) + " to contain B " + b);
}
//O(n*m^2)
private static int atimesbBruteForce(String a, String b) {
int n = a.length();
int m = b.length();
String tempA = a;
if (tempA.contains(b))
return 1;
for (int i = 1; i < m; i++) { // O(m)
tempA = tempA + a;
if (tempA.contains(b)) //O(n*m); since temp A length could be max "m" times a length which is "n", for checking contains it take O(textLength); O(m*n)
return i + 1;
}
return Integer.MIN_VALUE;
}
//Idea take from above stack overflow
//O((m^2)/n) -> i hope its right
private static int atimesb(String a, String b) {
int n = a.length();
int m = b.length();
if (m == 0)
return 0;
if (m == 1)
return (a.contains(b) ? 1 : -1);
int count;
if (m > 2 * n - 2) {
count = countTimes(b, a); // O(m/n)
if (count > 0) {
return count + atimesb(a, removeByTimes(b, a)); // O(m)
} else
return count;
} else if (m < n + 2) {
a = a + a;
count = countTimes(a, b); // O(m)
if (count > 0) {
return 1 + count;
} else
return Integer.MIN_VALUE;
} else {
a = a + a + a;
count = countTimes(a, b); // O(m)
if (count > 0)
return 3 - count;
else return Integer.MIN_VALUE;
}
}
private static String removeByTimes(String b, String a) {
return b.replaceAll(a, "");
}
/**
* It will count how many times "toCount" is occur in "fromCount" if occures at all
*
* #param fromToCount
* #param toCount
* #return How many times, otherwise 0 if not occur
*/
private static int countTimes(String fromToCount, String toCount) {
int count = 0;
while (fromToCount.contains(toCount)) {
fromToCount = fromToCount.replaceFirst(toCount, "");
count++;
}
return count;
}
}
Here is my solution in Python2 for the same. I followed mathematical way of solving the expression
def google(a,b):
x=(len(b)/len(a))+1
print x
google("abcd","cda")
Example:
Given “25525511135”
Output : [“255.255.11.135”, “255.255.111.35”]. (sorted order)
Kindly let me know if we could do a depth first search over here ?(that's the only thing striking me )
Why is it important to have an 'optimal' approach for answering this?
There are not many permutations so the simple approach of checking every combination that fits into the IP format and then filtering out those that have out of range numbers will easily work.
It's unlikely to be a bottle neck for whatever this is part of.
You probably want a dynamic programming algorithm for the general case (something like
http://www.geeksforgeeks.org/dynamic-programming-set-32-word-break-problem/).
Instead of testing whether prefixes can be segmented into words in the dictionary, you'd be testing to see whether the prefixes are prefixes of some valid IPv4 address.
Brutal DFS is acceptable in this problem:
class Solution{
private:
vector<string> ans;
int len;
string cur, rec, str;
bool IsOk(string s) {
if(s[0] == '0' && s.size() > 1) return false;
int sum = 0;
for(int i = 0; i < s.size(); i ++) {
if(s[i] == '.') return false;
sum = sum * 10 + s[i] - '0';
}
if(sum >= 0 && sum <= 255) return true;
return false;
}
void dfs(int x, int cnt) {
if(x == len) {
if(str.size() != len + 4) return ;
string tmp(str);
tmp.erase(tmp.size() - 1, 1);
if(cnt == 4) ans.push_back(tmp);
return ;
}
if(cnt > 4 || str.size() > len + 4) return ;
string tmp = cur;
cur += rec[x];
if(!IsOk(cur)) {
cur = tmp;
return ;
}
dfs(x + 1, cnt);
string tmp2 = cur + '.';
str += tmp2;
cur = "";
dfs(x + 1, cnt + 1);
str.erase(str.size() - tmp2.size(), tmp2.size());
cur = tmp;
}
public:
vector<string> restoreIpAddresses(string s) {
this->len = s.size();
this->rec = s;
cur = str = "";
ans.clear();
dfs(0, 0);
return ans;
}
};
Here is a recursive solution on JavaScript. The result is not sorted.
// Task from https://www.geeksforgeeks.org/program-generate-possible-valid-ip-addresses-given-string/
// Given a string containing only digits, restore it by returning all possible valid IP address combinations.
//
// Example:
// Input : 25525511135
// Output : [“255.255.11.135”, “255.255.111.35”]
//
(function () {
function getValidIP(str) {
const result = [];
const length = str.length;
check(0, 0, '');
function check(start, level, previous){
let i = 0;
let num;
if (level === 3) {
num = str.substring(start);
if (num && num < 256) {
result.push(`${previous}.${num}`);
}
return;
}
num = str.substring(start, start + 1);
if (num == 0) {
check(start + 1, level + 1, level === 0 ? `${num}`: `${previous}.${num}`);
} else {
while (num.length < 4 && num < 256 && start + i + 1 < length) {
check(start + i + 1, level + 1, level === 0 ? `${num}`: `${previous}.${num}`);
i++;
num = str.substring(start, start + i + 1);
}
}
}
return result;
}
console.log('12345:')
console.time('1-1');
console.log(getValidIP('12345'));
console.timeEnd('1-1');
console.log('1234:')
console.time('1-2');
console.log(getValidIP('1234'));
console.timeEnd('1-2');
console.log('2555011135:')
console.time('1-3');
console.log(getValidIP('2555011135'));
console.timeEnd('1-3');
console.log('222011135:')
console.time('1-4');
console.log(getValidIP('222011135'));
console.timeEnd('1-4');
})();
How do you convert a numerical number to an Excel column name in C# without using automation getting the value directly from Excel.
Excel 2007 has a possible range of 1 to 16384, which is the number of columns that it supports. The resulting values should be in the form of excel column names, e.g. A, AA, AAA etc.
Here's how I do it:
private string GetExcelColumnName(int columnNumber)
{
string columnName = "";
while (columnNumber > 0)
{
int modulo = (columnNumber - 1) % 26;
columnName = Convert.ToChar('A' + modulo) + columnName;
columnNumber = (columnNumber - modulo) / 26;
}
return columnName;
}
If anyone needs to do this in Excel without VBA, here is a way:
=SUBSTITUTE(ADDRESS(1;colNum;4);"1";"")
where colNum is the column number
And in VBA:
Function GetColumnName(colNum As Integer) As String
Dim d As Integer
Dim m As Integer
Dim name As String
d = colNum
name = ""
Do While (d > 0)
m = (d - 1) Mod 26
name = Chr(65 + m) + name
d = Int((d - m) / 26)
Loop
GetColumnName = name
End Function
You might need conversion both ways, e.g from Excel column adress like AAZ to integer and from any integer to Excel. The two methods below will do just that. Assumes 1 based indexing, first element in your "arrays" are element number 1.
No limits on size here, so you can use adresses like ERROR and that would be column number 2613824 ...
public static string ColumnAdress(int col)
{
if (col <= 26) {
return Convert.ToChar(col + 64).ToString();
}
int div = col / 26;
int mod = col % 26;
if (mod == 0) {mod = 26;div--;}
return ColumnAdress(div) + ColumnAdress(mod);
}
public static int ColumnNumber(string colAdress)
{
int[] digits = new int[colAdress.Length];
for (int i = 0; i < colAdress.Length; ++i)
{
digits[i] = Convert.ToInt32(colAdress[i]) - 64;
}
int mul=1;int res=0;
for (int pos = digits.Length - 1; pos >= 0; --pos)
{
res += digits[pos] * mul;
mul *= 26;
}
return res;
}
Sorry, this is Python instead of C#, but at least the results are correct:
def ColIdxToXlName(idx):
if idx < 1:
raise ValueError("Index is too small")
result = ""
while True:
if idx > 26:
idx, r = divmod(idx - 1, 26)
result = chr(r + ord('A')) + result
else:
return chr(idx + ord('A') - 1) + result
for i in xrange(1, 1024):
print "%4d : %s" % (i, ColIdxToXlName(i))
I discovered an error in my first post, so I decided to sit down and do the the math. What I found is that the number system used to identify Excel columns is not a base 26 system, as another person posted. Consider the following in base 10. You can also do this with the letters of the alphabet.
Space:.........................S1, S2, S3 : S1, S2, S3
....................................0, 00, 000 :.. A, AA, AAA
....................................1, 01, 001 :.. B, AB, AAB
.................................... …, …, … :.. …, …, …
....................................9, 99, 999 :.. Z, ZZ, ZZZ
Total states in space: 10, 100, 1000 : 26, 676, 17576
Total States:...............1110................18278
Excel numbers columns in the individual alphabetical spaces using base 26. You can see that in general, the state space progression is a, a^2, a^3, … for some base a, and the total number of states is a + a^2 + a^3 + … .
Suppose you want to find the total number of states A in the first N spaces. The formula for doing so is A = (a)(a^N - 1 )/(a-1). This is important because we need to find the space N that corresponds to our index K. If I want to find out where K lies in the number system I need to replace A with K and solve for N. The solution is N = log{base a} (A (a-1)/a +1). If I use the example of a = 10 and K = 192, I know that N = 2.23804… . This tells me that K lies at the beginning of the third space since it is a little greater than two.
The next step is to find exactly how far in the current space we are. To find this, subtract from K the A generated using the floor of N. In this example, the floor of N is two. So, A = (10)(10^2 – 1)/(10-1) = 110, as is expected when you combine the states of the first two spaces. This needs to be subtracted from K because these first 110 states would have already been accounted for in the first two spaces. This leaves us with 82 states. So, in this number system, the representation of 192 in base 10 is 082.
The C# code using a base index of zero is
private string ExcelColumnIndexToName(int Index)
{
string range = string.Empty;
if (Index < 0 ) return range;
int a = 26;
int x = (int)Math.Floor(Math.Log((Index) * (a - 1) / a + 1, a));
Index -= (int)(Math.Pow(a, x) - 1) * a / (a - 1);
for (int i = x+1; Index + i > 0; i--)
{
range = ((char)(65 + Index % a)).ToString() + range;
Index /= a;
}
return range;
}
//Old Post
A zero-based solution in C#.
private string ExcelColumnIndexToName(int Index)
{
string range = "";
if (Index < 0 ) return range;
for(int i=1;Index + i > 0;i=0)
{
range = ((char)(65 + Index % 26)).ToString() + range;
Index /= 26;
}
if (range.Length > 1) range = ((char)((int)range[0] - 1)).ToString() + range.Substring(1);
return range;
}
This answer is in javaScript:
function getCharFromNumber(columnNumber){
var dividend = columnNumber;
var columnName = "";
var modulo;
while (dividend > 0)
{
modulo = (dividend - 1) % 26;
columnName = String.fromCharCode(65 + modulo).toString() + columnName;
dividend = parseInt((dividend - modulo) / 26);
}
return columnName;
}
Easy with recursion.
public static string GetStandardExcelColumnName(int columnNumberOneBased)
{
int baseValue = Convert.ToInt32('A');
int columnNumberZeroBased = columnNumberOneBased - 1;
string ret = "";
if (columnNumberOneBased > 26)
{
ret = GetStandardExcelColumnName(columnNumberZeroBased / 26) ;
}
return ret + Convert.ToChar(baseValue + (columnNumberZeroBased % 26) );
}
I'm surprised all of the solutions so far contain either iteration or recursion.
Here's my solution that runs in constant time (no loops). This solution works for all possible Excel columns and checks that the input can be turned into an Excel column. Possible columns are in the range [A, XFD] or [1, 16384]. (This is dependent on your version of Excel)
private static string Turn(uint col)
{
if (col < 1 || col > 16384) //Excel columns are one-based (one = 'A')
throw new ArgumentException("col must be >= 1 and <= 16384");
if (col <= 26) //one character
return ((char)(col + 'A' - 1)).ToString();
else if (col <= 702) //two characters
{
char firstChar = (char)((int)((col - 1) / 26) + 'A' - 1);
char secondChar = (char)(col % 26 + 'A' - 1);
if (secondChar == '#') //Excel is one-based, but modulo operations are zero-based
secondChar = 'Z'; //convert one-based to zero-based
return string.Format("{0}{1}", firstChar, secondChar);
}
else //three characters
{
char firstChar = (char)((int)((col - 1) / 702) + 'A' - 1);
char secondChar = (char)((col - 1) / 26 % 26 + 'A' - 1);
char thirdChar = (char)(col % 26 + 'A' - 1);
if (thirdChar == '#') //Excel is one-based, but modulo operations are zero-based
thirdChar = 'Z'; //convert one-based to zero-based
return string.Format("{0}{1}{2}", firstChar, secondChar, thirdChar);
}
}
Same implementation in Java
public String getExcelColumnName (int columnNumber)
{
int dividend = columnNumber;
int i;
String columnName = "";
int modulo;
while (dividend > 0)
{
modulo = (dividend - 1) % 26;
i = 65 + modulo;
columnName = new Character((char)i).toString() + columnName;
dividend = (int)((dividend - modulo) / 26);
}
return columnName;
}
int nCol = 127;
string sChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
string sCol = "";
while (nCol >= 26)
{
int nChar = nCol % 26;
nCol = (nCol - nChar) / 26;
// You could do some trick with using nChar as offset from 'A', but I am lazy to do it right now.
sCol = sChars[nChar] + sCol;
}
sCol = sChars[nCol] + sCol;
Update: Peter's comment is right. That's what I get for writing code in the browser. :-) My solution was not compiling, it was missing the left-most letter and it was building the string in reverse order - all now fixed.
Bugs aside, the algorithm is basically converting a number from base 10 to base 26.
Update 2: Joel Coehoorn is right - the code above will return AB for 27. If it was real base 26 number, AA would be equal to A and the next number after Z would be BA.
int nCol = 127;
string sChars = "0ABCDEFGHIJKLMNOPQRSTUVWXYZ";
string sCol = "";
while (nCol > 26)
{
int nChar = nCol % 26;
if (nChar == 0)
nChar = 26;
nCol = (nCol - nChar) / 26;
sCol = sChars[nChar] + sCol;
}
if (nCol != 0)
sCol = sChars[nCol] + sCol;
..And converted to php:
function GetExcelColumnName($columnNumber) {
$columnName = '';
while ($columnNumber > 0) {
$modulo = ($columnNumber - 1) % 26;
$columnName = chr(65 + $modulo) . $columnName;
$columnNumber = (int)(($columnNumber - $modulo) / 26);
}
return $columnName;
}
Just throwing in a simple two-line C# implementation using recursion, because all the answers here seem far more complicated than necessary.
/// <summary>
/// Gets the column letter(s) corresponding to the given column number.
/// </summary>
/// <param name="column">The one-based column index. Must be greater than zero.</param>
/// <returns>The desired column letter, or an empty string if the column number was invalid.</returns>
public static string GetColumnLetter(int column) {
if (column < 1) return String.Empty;
return GetColumnLetter((column - 1) / 26) + (char)('A' + (column - 1) % 26);
}
Although there are already a bunch of valid answers1, none get into the theory behind it.
Excel column names are bijective base-26 representations of their number. This is quite different than an ordinary base 26 (there is no leading zero), and I really recommend reading the Wikipedia entry to grasp the differences. For example, the decimal value 702 (decomposed in 26*26 + 26) is represented in "ordinary" base 26 by 110 (i.e. 1x26^2 + 1x26^1 + 0x26^0) and in bijective base-26 by ZZ (i.e. 26x26^1 + 26x26^0).
Differences aside, bijective numeration is a positional notation, and as such we can perform conversions using an iterative (or recursive) algorithm which on each iteration finds the digit of the next position (similarly to an ordinary base conversion algorithm).
The general formula to get the digit at the last position (the one indexed 0) of the bijective base-k representation of a decimal number m is (f being the ceiling function minus 1):
m - (f(m / k) * k)
The digit at the next position (i.e. the one indexed 1) is found by applying the same formula to the result of f(m / k). We know that for the last digit (i.e. the one with the highest index) f(m / k) is 0.
This forms the basis for an iteration that finds each successive digit in bijective base-k of a decimal number. In pseudo-code it would look like this (digit() maps a decimal integer to its representation in the bijective base -- e.g. digit(1) would return A in bijective base-26):
fun conv(m)
q = f(m / k)
a = m - (q * k)
if (q == 0)
return digit(a)
else
return conv(q) + digit(a);
So we can translate this to C#2 to get a generic3 "conversion to bijective base-k" ToBijective() routine:
class BijectiveNumeration {
private int baseK;
private Func<int, char> getDigit;
public BijectiveNumeration(int baseK, Func<int, char> getDigit) {
this.baseK = baseK;
this.getDigit = getDigit;
}
public string ToBijective(double decimalValue) {
double q = f(decimalValue / baseK);
double a = decimalValue - (q * baseK);
return ((q > 0) ? ToBijective(q) : "") + getDigit((int)a);
}
private static double f(double i) {
return (Math.Ceiling(i) - 1);
}
}
Now for conversion to bijective base-26 (our "Excel column name" use case):
static void Main(string[] args)
{
BijectiveNumeration bijBase26 = new BijectiveNumeration(
26,
(value) => Convert.ToChar('A' + (value - 1))
);
Console.WriteLine(bijBase26.ToBijective(1)); // prints "A"
Console.WriteLine(bijBase26.ToBijective(26)); // prints "Z"
Console.WriteLine(bijBase26.ToBijective(27)); // prints "AA"
Console.WriteLine(bijBase26.ToBijective(702)); // prints "ZZ"
Console.WriteLine(bijBase26.ToBijective(16384)); // prints "XFD"
}
Excel's maximum column index is 16384 / XFD, but this code will convert any positive number.
As an added bonus, we can now easily convert to any bijective base. For example for bijective base-10:
static void Main(string[] args)
{
BijectiveNumeration bijBase10 = new BijectiveNumeration(
10,
(value) => value < 10 ? Convert.ToChar('0'+value) : 'A'
);
Console.WriteLine(bijBase10.ToBijective(1)); // prints "1"
Console.WriteLine(bijBase10.ToBijective(10)); // prints "A"
Console.WriteLine(bijBase10.ToBijective(123)); // prints "123"
Console.WriteLine(bijBase10.ToBijective(20)); // prints "1A"
Console.WriteLine(bijBase10.ToBijective(100)); // prints "9A"
Console.WriteLine(bijBase10.ToBijective(101)); // prints "A1"
Console.WriteLine(bijBase10.ToBijective(2010)); // prints "19AA"
}
1 This generic answer can eventually be reduced to the other, correct, specific answers, but I find it hard to fully grasp the logic of the solutions without the formal theory behind bijective numeration in general. It also proves its correctness nicely. Additionally, several similar questions link back to this one, some being language-agnostic or more generic. That's why I thought the addition of this answer was warranted, and that this question was a good place to put it.
2 C# disclaimer: I implemented an example in C# because this is what is asked here, but I have never learned nor used the language. I have verified it does compile and run, but please adapt it to fit the language best practices / general conventions, if necessary.
3 This example only aims to be correct and understandable ; it could and should be optimized would performance matter (e.g. with tail-recursion -- but that seems to require trampolining in C#), and made safer (e.g. by validating parameters).
I wanted to throw in my static class I use, for interoping between col index and col Label. I use a modified accepted answer for my ColumnLabel Method
public static class Extensions
{
public static string ColumnLabel(this int col)
{
var dividend = col;
var columnLabel = string.Empty;
int modulo;
while (dividend > 0)
{
modulo = (dividend - 1) % 26;
columnLabel = Convert.ToChar(65 + modulo).ToString() + columnLabel;
dividend = (int)((dividend - modulo) / 26);
}
return columnLabel;
}
public static int ColumnIndex(this string colLabel)
{
// "AD" (1 * 26^1) + (4 * 26^0) ...
var colIndex = 0;
for(int ind = 0, pow = colLabel.Count()-1; ind < colLabel.Count(); ++ind, --pow)
{
var cVal = Convert.ToInt32(colLabel[ind]) - 64; //col A is index 1
colIndex += cVal * ((int)Math.Pow(26, pow));
}
return colIndex;
}
}
Use this like...
30.ColumnLabel(); // "AD"
"AD".ColumnIndex(); // 30
private String getColumn(int c) {
String s = "";
do {
s = (char)('A' + (c % 26)) + s;
c /= 26;
} while (c-- > 0);
return s;
}
Its not exactly base 26, there is no 0 in the system. If there was, 'Z' would be followed by 'BA' not by 'AA'.
if you just want it for a cell formula without code, here's a formula for it:
IF(COLUMN()>=26,CHAR(ROUND(COLUMN()/26,1)+64)&CHAR(MOD(COLUMN(),26)+64),CHAR(COLUMN()+64))
In Delphi (Pascal):
function GetExcelColumnName(columnNumber: integer): string;
var
dividend, modulo: integer;
begin
Result := '';
dividend := columnNumber;
while dividend > 0 do begin
modulo := (dividend - 1) mod 26;
Result := Chr(65 + modulo) + Result;
dividend := (dividend - modulo) div 26;
end;
end;
A little late to the game, but here's the code I use (in C#):
private static readonly string _Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
public static int ColumnNameParse(string value)
{
// assumes value.Length is [1,3]
// assumes value is uppercase
var digits = value.PadLeft(3).Select(x => _Alphabet.IndexOf(x));
return digits.Aggregate(0, (current, index) => (current * 26) + (index + 1));
}
In perl, for an input of 1 (A), 27 (AA), etc.
sub excel_colname {
my ($idx) = #_; # one-based column number
--$idx; # zero-based column index
my $name = "";
while ($idx >= 0) {
$name .= chr(ord("A") + ($idx % 26));
$idx = int($idx / 26) - 1;
}
return scalar reverse $name;
}
Though I am late to the game, Graham's answer is far from being optimal. Particularly, you don't have to use the modulo, call ToString() and apply (int) cast. Considering that in most cases in C# world you would start numbering from 0, here is my revision:
public static string GetColumnName(int index) // zero-based
{
const byte BASE = 'Z' - 'A' + 1;
string name = String.Empty;
do
{
name = Convert.ToChar('A' + index % BASE) + name;
index = index / BASE - 1;
}
while (index >= 0);
return name;
}
More than 30 solutions already, but here's my one-line C# solution...
public string IntToExcelColumn(int i)
{
return ((i<16926? "" : ((char)((((i/26)-1)%26)+65)).ToString()) + (i<2730? "" : ((char)((((i/26)-1)%26)+65)).ToString()) + (i<26? "" : ((char)((((i/26)-1)%26)+65)).ToString()) + ((char)((i%26)+65)));
}
After looking at all the supplied Versions here, I decided to do one myself, using recursion.
Here is my vb.net Version:
Function CL(ByVal x As Integer) As String
If x >= 1 And x <= 26 Then
CL = Chr(x + 64)
Else
CL = CL((x - x Mod 26) / 26) & Chr((x Mod 26) + 1 + 64)
End If
End Function
Refining the original solution (in C#):
public static class ExcelHelper
{
private static Dictionary<UInt16, String> l_DictionaryOfColumns;
public static ExcelHelper() {
l_DictionaryOfColumns = new Dictionary<ushort, string>(256);
}
public static String GetExcelColumnName(UInt16 l_Column)
{
UInt16 l_ColumnCopy = l_Column;
String l_Chars = "0ABCDEFGHIJKLMNOPQRSTUVWXYZ";
String l_rVal = "";
UInt16 l_Char;
if (l_DictionaryOfColumns.ContainsKey(l_Column) == true)
{
l_rVal = l_DictionaryOfColumns[l_Column];
}
else
{
while (l_ColumnCopy > 26)
{
l_Char = l_ColumnCopy % 26;
if (l_Char == 0)
l_Char = 26;
l_ColumnCopy = (l_ColumnCopy - l_Char) / 26;
l_rVal = l_Chars[l_Char] + l_rVal;
}
if (l_ColumnCopy != 0)
l_rVal = l_Chars[l_ColumnCopy] + l_rVal;
l_DictionaryOfColumns.ContainsKey(l_Column) = l_rVal;
}
return l_rVal;
}
}
Here is an Actionscript version:
private var columnNumbers:Array = ['A', 'B', 'C', 'D', 'E', 'F' , 'G', 'H', 'I', 'J', 'K' ,'L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];
private function getExcelColumnName(columnNumber:int) : String{
var dividend:int = columnNumber;
var columnName:String = "";
var modulo:int;
while (dividend > 0)
{
modulo = (dividend - 1) % 26;
columnName = columnNumbers[modulo] + columnName;
dividend = int((dividend - modulo) / 26);
}
return columnName;
}
JavaScript Solution
/**
* Calculate the column letter abbreviation from a 1 based index
* #param {Number} value
* #returns {string}
*/
getColumnFromIndex = function (value) {
var base = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
var remainder, result = "";
do {
remainder = value % 26;
result = base[(remainder || 26) - 1] + result;
value = Math.floor(value / 26);
} while (value > 0);
return result;
};
These my codes to convert specific number (index start from 1) to Excel Column.
public static string NumberToExcelColumn(uint number)
{
uint originalNumber = number;
uint numChars = 1;
while (Math.Pow(26, numChars) < number)
{
numChars++;
if (Math.Pow(26, numChars) + 26 >= number)
{
break;
}
}
string toRet = "";
uint lastValue = 0;
do
{
number -= lastValue;
double powerVal = Math.Pow(26, numChars - 1);
byte thisCharIdx = (byte)Math.Truncate((columnNumber - 1) / powerVal);
lastValue = (int)powerVal * thisCharIdx;
if (numChars - 2 >= 0)
{
double powerVal_next = Math.Pow(26, numChars - 2);
byte thisCharIdx_next = (byte)Math.Truncate((columnNumber - lastValue - 1) / powerVal_next);
int lastValue_next = (int)Math.Pow(26, numChars - 2) * thisCharIdx_next;
if (thisCharIdx_next == 0 && lastValue_next == 0 && powerVal_next == 26)
{
thisCharIdx--;
lastValue = (int)powerVal * thisCharIdx;
}
}
toRet += (char)((byte)'A' + thisCharIdx + ((numChars > 1) ? -1 : 0));
numChars--;
} while (numChars > 0);
return toRet;
}
My Unit Test:
[TestMethod]
public void Test()
{
Assert.AreEqual("A", NumberToExcelColumn(1));
Assert.AreEqual("Z", NumberToExcelColumn(26));
Assert.AreEqual("AA", NumberToExcelColumn(27));
Assert.AreEqual("AO", NumberToExcelColumn(41));
Assert.AreEqual("AZ", NumberToExcelColumn(52));
Assert.AreEqual("BA", NumberToExcelColumn(53));
Assert.AreEqual("ZZ", NumberToExcelColumn(702));
Assert.AreEqual("AAA", NumberToExcelColumn(703));
Assert.AreEqual("ABC", NumberToExcelColumn(731));
Assert.AreEqual("ACQ", NumberToExcelColumn(771));
Assert.AreEqual("AYZ", NumberToExcelColumn(1352));
Assert.AreEqual("AZA", NumberToExcelColumn(1353));
Assert.AreEqual("AZB", NumberToExcelColumn(1354));
Assert.AreEqual("BAA", NumberToExcelColumn(1379));
Assert.AreEqual("CNU", NumberToExcelColumn(2413));
Assert.AreEqual("GCM", NumberToExcelColumn(4823));
Assert.AreEqual("MSR", NumberToExcelColumn(9300));
Assert.AreEqual("OMB", NumberToExcelColumn(10480));
Assert.AreEqual("ULV", NumberToExcelColumn(14530));
Assert.AreEqual("XFD", NumberToExcelColumn(16384));
}
Sorry, this is Python instead of C#, but at least the results are correct:
def excel_column_number_to_name(column_number):
output = ""
index = column_number-1
while index >= 0:
character = chr((index%26)+ord('A'))
output = output + character
index = index/26 - 1
return output[::-1]
for i in xrange(1, 1024):
print "%4d : %s" % (i, excel_column_number_to_name(i))
Passed these test cases:
Column Number: 494286 => ABCDZ
Column Number: 27 => AA
Column Number: 52 => AZ
For what it is worth, here is Graham's code in Powershell:
function ConvertTo-ExcelColumnID {
param (
[parameter(Position = 0,
HelpMessage = "A 1-based index to convert to an excel column ID. e.g. 2 => 'B', 29 => 'AC'",
Mandatory = $true)]
[int]$index
);
[string]$result = '';
if ($index -le 0 ) {
return $result;
}
while ($index -gt 0) {
[int]$modulo = ($index - 1) % 26;
$character = [char]($modulo + [int][char]'A');
$result = $character + $result;
[int]$index = ($index - $modulo) / 26;
}
return $result;
}
Another VBA way
Public Function GetColumnName(TargetCell As Range) As String
GetColumnName = Split(CStr(TargetCell.Cells(1, 1).Address), "$")(1)
End Function
Here's my super late implementation in PHP. This one's recursive. I wrote it just before I found this post. I wanted to see if others had solved this problem already...
public function GetColumn($intNumber, $strCol = null) {
if ($intNumber > 0) {
$intRem = ($intNumber - 1) % 26;
$strCol = $this->GetColumn(intval(($intNumber - $intRem) / 26), sprintf('%s%s', chr(65 + $intRem), $strCol));
}
return $strCol;
}