LeetCode - 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],]

class Solution {public:    void combine(vector<vector<int> >& result,vector<int>& num,int begin,int n,int k){if(k==0){result.push_back(num);return;}for(int i=begin;i<=n;i++){num.push_back(i);combine(result,num,i+1,n,k-1);num.pop_back();}}vector<vector<int> > combine(int n, int k) {vector<vector<int> > result;if(n<=0||n<k||k<=0){return result;}vector<int> num;combine(result,num,1,n,k);return result;}};