c# - Getting all possible combinations from a list of numbers -

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i'm looking efficient way achieve this:

  • you have list of numbers 1.....n (typically: 1..5 or 1..7 or - reasonably small, can vary case case)

  • you need combinations of lengths numbers, e.g. combinations of 1 number ({1}, {2}, .... {n}), combinations of 2 distinct numbers ({1,2}, {1,3}, {1,4} ..... {n-1, n} ), combinations fo 3 of numbers ({1,2,3}, {1,2,4}) , forth

basically, within group, order irrelevant, {1,2,3} equivalent {1,3,2} - it's matter of getting groups of x numbers list

seems there ought simple algorithm - have searched in vain far. combinatorics , permutation algorithms seems a) take order account (e.g. 123 not equal 132), , seems operate on single string of characters or numbers....

anyone have great, nice'n'quick algorithm sleeve??

thanks!

just increment binary number , take elements corresponding bits set.

for instance, 00101101 mean take elements @ indexes 0, 2, 3, , 5. since list 1..n, element index + 1.

this generate in-order permuatations. in other words, {1, 2, 3} generated. not {1, 3, 2} or {2, 1, 3} or {2, 3, 1}, etc.


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