[*] Combination

title :

Given-integers n and K, return all possible combinations of K numbers out of 1 ... n.

For example,
If N = 4 and k = 2, a solution is:

[  [2,4],  [3,4], [  2,3],  [up],  [1,3],  [1,4],]

Exercises

This problem is solved by using DFS (reference work breakii) as a method of cyclic recursive processing of sub-problems. n is the number of cycles, and K is a different number for each attempt. Use of backtracking.

The code is as follows:

1  PublicArraylist<arraylist<integer>> Combine (intNintk) {2arraylist<arraylist<integer>> res =NewArraylist<arraylist<integer>>();3         if(N <= 0| | N <k)4             returnRes;5arraylist<integer> item =NewArraylist<integer>(); 6DFS (N,k,1,item, res);//because it need to begin from 17         returnRes;8     }9     Private voidDfsintNintKintStart, arraylist<integer> item, arraylist<arraylist<integer>>Res) {Ten         if(item.size () = =k) { OneRes.add (NewArraylist<integer> (item));//because item is arraylist<t> so it would not be disappear from the stack to stack A             return; -         } -          for(inti=start;i<=n;i++){ the Item.add (i); -DFS (n,k,i+1, item,res); -Item.remove (Item.size ()-1); -         } +}

reference:http://blog.csdn.net/linhuanmars/article/details/21260217

Http://www.cnblogs.com/springfor/p/3877168.html

[*] Combination