LeetCode_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:
    void  DFS(vector<int> &candidates, int target, int start, int sum, vector<int> &tp){
		if(sum == target){
			res.push_back(tp);
			return;
		}
		for(int i = start; i< candidates.size(); ++i){
			if(candidates[i] + sum <= target){
				tp.push_back(candidates[i]);
				DFS(candidates, target, i, sum+candidates[i], tp);
				tp.pop_back();
			}
		}
	}
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        res.clear();
		int len = candidates.size();
		if(len < 1 || target <1) return res;
		sort(candidates.begin(), candidates.end());
		vector<int> tp;
		DFS(candidates, target, 0, 0, tp);
		return res;
		
    }
private:
	vector<vector<int>> res;
};