I am looking for a sorting algorithm to help me in my work. My objective is the following: after receiving an input of this kind:
5 4
1 2
2 3
3 4
4 5
The first line tells me how many ids I have, and the second number tells me how many connections. The following lines tell me the connections, and tell me that the first Id comes before the second one, for example: 1 comes before 2, 2 comes before 3, and so on. And if an impossible situation occurs:
3 2
1 2
2 3
3 1
or
2 2
1 2
2 1
I want to be able to send an error message.
Is there an algorithm that already does this? or can u give me some guide lines to how to start my work? I do not want ur code just some help/tips/advices. Thanks in advance for ur time.
From your description, I think you are probably looking for topological sorting.
It is based on the assumption that 'impossible situation' occurs when one connections suggests that A comes before B but there is some another connection which suggests that B comes before A.
Link for topological sort:
Topological Sorting
Related
I have some input data like this.
unique ID
Q1
Q2
Q3
1
1
1
2
2
1
1
2
3
1
0
3
4
2
0
1
5
3
1
2
6
4
1
3
And my target is to extract some data which satisfy the following conditions:
total count: 4
Q1=1 count: 2
Q1=2 count: 1
Q2=1 count: 1~3
Q3=1 count: 1
In this case, both data set with ids [1, 2, 4, 5] or [2, 3, 4, 5] are acceptable answers.
In reality, I will possibly have 6000+ rows of data and up to 12 count limitation like above. The count might varies from 1 to 50.
I've written a solution which firstly group all ids by each condition, then use deapth first search to exhaustedly try out all possible combinations between the groups. (I believe this is a brute-force solution...)
However, I always run out my computer's memory and my time before I can get a possible answer.
My question is,
what's the possible least time complexity of this problem. (I believe this is kind of subset sum problem, but I am not sure)
how can I solve this problem instead of a brute-force one? I'm considering dynamic programming or decision tree. However, I believe that I will possibly run out of my computer's memory with either of this one. Or can I solve this problem by each data row's probabilities/entropy (and I would appreciate more details on this)?
My brute-force solution sample codes are not worth reading at all. Thus, I'll skip posting my code snippets...
I need a way to find pattern in list of values. In particular every second I get a value in a range (ex. 1-3), and I want to find recurring pattern from this value list.
If i plot this values into an x,y system i'd get something like a Nyquist–Shannon sampling. It could be very interesting to work on this.
I could also plot these values and work on visual pattern recognition (neural networks...).
input:
instant value
1 1
2 2
3 3
4 1
5 2
6 3
7 1
output->1,2,3
What could be the best way to proceed ?
Consider a DVR recorder that has the duty to record television programs.
Each program has a starting time and ending time.
The DVR has the following restrictions:
It may only record up to two items at once.
If it chooses to record an item, it must record it from start to end.
Given the the number of television programs and their starting/ending times, what is the maximum number of programs the DVR can record?
For example: Consider 6 programs:
They are written in the form:
a b c. a is the program number, b is starting time, and c is ending time
1 0 3
2 6 7
3 3 10
4 1 5
5 2 8
6 1 9
The optimal way to record is have programs 1 and 3 recorded back to back, and programs 2 and 4 recorded back to back. 2 and 4 will be recording alongside 1 and 3.
This means the max number of programs is 4.
What is an efficient algorithm to find the max number of programs that can be recorded?
This is a classic example for a greedy algorithm.
You create an array with tuples for each program in the input.
Now you sort this array by the end times and start going from the left to the right. If you can take the very next program (you are recording at most one program already), you increment the result counter and remember the end-time. For another program again fill the available slot if possible, if not, you can't record it and can discard it.
This way you will get the maximum number of programs that can be recorded in O(nlogn) time.
I am stuck on this problem for quite a while, it is basically reverse engineering bulls and cow game.
Read more here: http://rosettacode.org/wiki/Bulls_and_cows
I am not able to develop a logic for the problem given below, if you can think of a solving approach please comment the same.
Problem Statement:
Given few clue words(of form ABCD/DBCA etc) and the number of cows and bulls for each word,program
should be able to work out the actual word by evaluating the given clue words and generate the output secret word.
TEST CASES:
Input:
4
DBCC 0 2
CDAB 2 1
CAAD 1 2
CDDA 2 0
Output:
BDAA
The idea is to reduce the space of possible solutions. Before you start, all 4^4 combinations are possible. After you read the first clue [DBCC 0 2 ], you can eliminate a number of possible solutions, in this particular example you can eliminate all states which have a D in the first place, all which have a B in the second place and so on. Just eliminate all possible solutions which do not "fit" the current clue.
Do this with each clue, until only one solution is left. Another interesting problem of course is how to generate good clue patterns.
The way I did it is:
1. Generate all possible words, put them in a list (array)
2. Randomly select one of them (first question)and ask for clues
3. Take the answer (let's say it is 2,1)
4. Start comparing that question with
first, second, ..., to the last word from the list
5. if they give the same clue: count them, plac
i am programming a card game and i need to sort a stack of cards by their rank. so that they form a gapless sequence.
in this special game the card with value 2 could be used as a wild card, so for example the cards
2 3 5
should be sorted like this
3 2 5
because the 2 replaces the 4, otherwise it would not be a valid sequence.
however the cards
2 3 4
should stay like they are.
restriction: there an be only one '2' used as a wildcard.
2 2 3 4
would also stay like it is, because the first 2 would replace the ACE (or 1, whatever you call it).
the following would not be a valid input sequence, since one of the 2s must be use as a wildcard and one not. it is not possible to make up a gapless sequence then.
2 4 2 6
now i have a difficulty to figure out if a 2 is used as a wildcard or not. once i got that, i think i can do the rest of the sorting
thanks for any algorithmic help on this problem!
EDIT in response to your clarification to your new requirement:
You're implying that you'll never get data for which a gapless sequence cannot be formed. (If only I could have such guarantees in the real world.) So:
Do you have a 2?
No: your sequence must already be gapless.
Yes: You need to figure out where to put it.
Sort your input. Do you see a gap? Since you can only use one 2 as a wildcard, there can be at most one gap.
No: treat the 2 as a legitimate number two.
Yes: move the 2 to the gap to fill it in.
EDIT in response to your new requirement:
In this case, just look for the highest single gap, and plug it with a 2 if you have a 2 available.
Original answer:
Since your sequence must be gapless, you could count the number of 2s you have and the sizes of all the gaps that are present. Then just fill in the highest gap for which you have a sufficient number of 2s.