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], ]
public class Solution { List<List<Integer>> res; List<Integer> seq; public List<List<Integer>> combine(int n, int k) { //注意分析题意，可选数组时从1到n，因此起始findCom函数的start参数需要从1开始 res=new ArrayList<List<Integer>>(); seq=new ArrayList<Integer>(); findCom(n,1,0,k); return res; } public void findCom(int n,int start,int level,int k){ if(level==k){ res.add(new ArrayList<Integer>(seq)); return; } for(int i=start;i<=n;i++){//注意i可以为n seq.add(i); findCom(n,i+1,level+1,k); seq.remove(seq.size()-1); } } }
原文：http://www.cnblogs.com/qiaomu/p/4646394.html