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, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
• 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] 

class Solution {public:vector<vector<int> > res;    vector<vector<int> > combinationSum(vector<int> &candidates, int target){res.clear();vector<int> path;sort(candidates.begin(), candidates.end());execute(candidates, target, 0, path);return res;    }void execute(vector<int> &candidates, int target, int pos, vector<int>& path){for (int i = pos; i < candidates.size(); i++){if(candidates[i] > target)return;path.push_back(candidates[i]);if(candidates[i] == target){res.push_back(path);path.pop_back();return;}elseexecute(candidates, target - candidates[i], i, path);path.pop_back();}}};