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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], ]
class Solution { public: vector<vector<int>> combine(int n, int k) { vector<vector<int>> res; vector<int> tmp; helper(res,tmp,n,k,1); return res; } void helper(vector<vector<int>> &res,vector<int> &tmp,int n,int k,int num){ if(k==0){ res.push_back(tmp); return; } for(int i=num;i<=n-k+1;++i){ tmp.push_back(i); helper(res,tmp,n,k-1,i+1); tmp.pop_back(); } } };
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原文地址：http://www.cnblogs.com/michaelzhao10/p/4906422.html
