#Leetcode# 39. Combination Sum

https://leetcode.com/problems/combination-sum/

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) {
        int n = candidates.size();
        vector<int> out;
        vector<vector<int> > ans;
        dfs(candidates, target, 0, ans, out);
        return ans;
    }
    void dfs(vector<int> &candidates, int target, int st, vector<vector<int>> &ans, vector<int> &out) {
        if(target < 0) return ;
        else if(target == 0) {ans.push_back(out); return ;}
        for(int i = st; i < candidates.size(); i ++) {
                out.push_back(candidates[i]);
                dfs(candidates, target - candidates[i], i, ans, out);
                out.pop_back();
        }
    }
};