Combinations

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     public ArrayList<ArrayList<Integer>> combine(int n, int k) {
 3         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
 4         get(n,k,1,new ArrayList<Integer>(),res);
 5         return res;
 6     }
 7     public void get(int n,int k,int start,ArrayList<Integer>output,ArrayList<ArrayList<Integer>>res){
 8         if(output.size()==k){
 9             ArrayList<Integer> temp = new ArrayList<Integer>();
10             temp.addAll(output);
11             res.add(temp);
12             return;
13         }
14         for(int i=start;i<=n;i++){
15             output.add(i);
16             get(n,k,i+1,output,res);
17             output.remove(output.size()-1);
18         }
19     }
20 }
View Code

 

posted @ 2014-02-06 14:38  krunning  阅读(114)  评论(0)  编辑  收藏  举报