Find i-th combination of an array

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Hi,
The problem is that I am given an array in the first combination and I have to find i-th combination of this array. (0 < i < total combinations)

Total number of combinations could be large and I don't want to find the combinations from 2nd to (i-1)-th.
I just want to know the i-th combination immediately.

Please give me some advance.

Thanks

Posted 24-May-12 10:48am

Duc Huy Nguyen

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Espen Harlinn · Answer 1 · 2012-05-24T12:37:00

Solution 2

I guess you are looking for bool next_permutation[^]

Call it i times and you'll have the i-th permutation. (or the i-1 combination)

Best regards
Espen Harlinn

Posted 24-May-12 12:37pm

Espen Harlinn

Comments

Sandeep Mewara 25-May-12 0:56am

My 5!

Espen Harlinn 25-May-12 3:29am

Thank you, Sandeep :-D

Duc Huy Nguyen 25-May-12 15:17pm

The problem í that I don't want to call the method for i times :)

Clifford Nelson · Answer 2 · 2012-05-24T11:57:00

First I would figure out if there is someway to sort the array so that it can be determined if the combination required if above or below the a selected combination they you can basically check if the match is above or below the center point, then above or below the center of either the top or the bottom of the array. This is called a binary search: http://en.wikipedia.org/wiki/Binary_search[^]