77. Combinations java solutions

Given two 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],
  [1,2],
  [1,3],
  [1,4],
]

 

 1 public class Solution {
 2     List<List<Integer>> ans = new ArrayList<List<Integer>>();
 3     public List<List<Integer>> combine(int n, int k) {
 4         List<Integer> list = new ArrayList<>();
 5         combination(list,n,k,1);
 6         return ans;
 7     }
 8     
 9     public void combination(List<Integer> list, int n, int k,int s){
10         if(k == 0){
11             List<Integer> tmp = new ArrayList<>(list);
12             ans.add(tmp);
13             return;
14         }
15         for(int i = s; i <= n; i++){
16             list.add(i);
17             combination(list,n,k-1,i+1);
18             list.remove(list.size()-1);
19         }
20     }
21 }

 

posted @ 2016-07-14 11:00  Miller1991  阅读(174)  评论(0)  编辑  收藏  举报