回溯Leetcode 39 Combination Sum

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Leetcode 39

Combination Sum

• Problem Description：
  经典回溯问题：给出一个集合，选取集合中的元素相加使得和等于给定的target值，返回所有满足情况的组合（对于同个元素可重复相加）
  具体的题目信息：
  https://leetcode.com/problems/combination-sum/description/
• Example:
  
• Solution:

class Solution {
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        vector<vector<int>> res;
        vector<int> t;
        sort(candidates.begin(), candidates.end());
        combination(t, res, 0, candidates, target);
        return res;
    }
    void combination(vector<int>&t, vector<vector<int>>& res, int i, vector<int>& candidates, int target) {
        if (target<0) {
            return;
        } else if (target == 0) {
            res.push_back(t);
            return;
        } else {
            for (int j = i; j < candidates.size(); j++) {
                t.push_back(candidates[j]);
                combination(t, res, j, candidates, target-candidates[j]);
                t.erase(t.begin()+t.size()-1);
            }
        }
    }
};