题目：

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.

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

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations.

Example 1:

Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
  [7],
  [2,2,3]
]

Example 2:

Input: candidates = [2,3,5], target = 8,
A solution set is:
[
  [2,2,2,2],
  [2,3,3],
  [3,5]
]

代码：

class Solution {
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        vector<vector<int>> res;
        deal(res, candidates, vector<int>(0), 0, target);
        return res;
    }
    
    void deal(vector<vector<int> >& res, vector<int>& candidates, vector<int> temp, int index, int target){
        if(target == 0){
            res.push_back(temp);
            return ;
        }
        else if(target < 0){
            return;
        }
        for(int i = index; i < candidates.size(); i++){
            temp.push_back(candidates[i]);
            deal(res, candidates, temp, i, target-candidates[i]);
            temp.pop_back();
        }
        
    }
};