Combination Sum

Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

The same repeated number may be chosen from C unlimited number of times.

Note:

• All numbers (including target) will be positive integers.
• Elements in a combination (a₁, a₂, � , a_k) must be in non-descending order. (ie, a₁ ? a₂ ? � ? a_k).
• The solution set must not contain duplicate combinations.

For example, given candidate set 2,3,6,7 and target 7, 
A solution set is: 
[7] 
[2, 2, 3] 

#include <algorithm>class Solution {public:    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {        // Start typing your C/C++ solution below        // DO NOT write int main() function    vector<vector<int> > result;vector<int> tmp;std::sort(candidates.begin(),candidates.end());combinationSum(candidates,0,target,result,tmp);return result;    }void  combinationSum(const vector<int> &candidates, int start,int target,   vector<vector<int> >& result,vector<int>& tmp) {for(int i=start;i<candidates.size();i++){int left=target-candidates[i];if(left<0)return ;if(left==0){tmp.push_back(candidates[i]);result.push_back(tmp);tmp.pop_back();return;}tmp.push_back(candidates[i]);combinationSum(candidates,i,left,result,tmp);tmp.pop_back();}return; }};