leetcode Combination Sum解题报告

偏执的太偏执、 2022-08-09 11:57 142阅读 0赞

# 题目 #

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:  
\[7\]  
\[2, 2, 3\]  
题目来源：[https://leetcode.com/problems/combination-sum/][https_leetcode.com_problems_combination-sum]

# 分析 #

回朔法。

# 代码 #

class Solution {
    private:
        vector<vector<int>> ans;
    public:
        void combinationSumHelp(vector<int>& candidates, int target, int start, vector<int>& tmpComb) {
            if(target == 0){
                ans.push_back(tmpComb);
                return;
            }
            if(target < 0)
                return;
            int len = candidates.size();
            for(int i = start; i < len; i++){
                tmpComb.push_back(candidates.at(i));
                combinationSumHelp(candidates, target - candidates.at(i), i, tmpComb);
                tmpComb.pop_back();
            }
        }
        vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
            sort(candidates.begin(), candidates.end());
            vector<int> tmpComb;
            combinationSumHelp(candidates, target, 0, tmpComb);
            return ans;
        }
    };

[https_leetcode.com_problems_combination-sum]: https://leetcode.com/problems/combination-sum/