Leetcode 39. Combination Sum-优快云博客

本文链接：https://blog.youkuaiyun.com/Quincuntial/article/details/83095682

本文深入探讨了组合求和问题的三种解决方案，通过详细的代码示例，讲解了如何使用递归算法找到所有可能的组合，使得这些组合中的元素之和等于目标值。文章提供了三个不同版本的C++实现，帮助读者理解并掌握这一复杂但实用的算法。

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文章作者：Tyan
博客：noahsnail.com | 优快云 | 简书

1. Description

Combination Sum

2. Solution

Version 1

class Solution {
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        set<vector<int>> s;
        sort(candidates.begin(), candidates.end());
        vector<int> combination;
        combinationSum(s, candidates, target, 0, combination);
        return vector<vector<int>>(s.begin(), s.end());
    }


private:
    void combinationSum(set<vector<int>>& result, vector<int>& candidates, int& target, int sum, vector<int> combination) {
        if(sum > target) {
            return;
        }
        if(sum == target) {
            sort(combination.begin(), combination.end());
            result.insert(combination);
            return;
        }
        for(int i = 0; i < candidates.size(); i++) {
            combination.push_back(candidates[i]);
            combinationSum(result, candidates, target, sum + candidates[i], combination);
            combination.pop_back();
        }
    }
};

Version 2

class Solution {
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        vector<vector<int>> result;
        sort(candidates.begin(), candidates.end());
        vector<int> combination;
        combinationSum(result, candidates, combination, target, 0, 0);
        return result;
    }

private:
    void combinationSum(vector<vector<int>>& result, vector<int>& candidates, vector<int> combination, int& target, int sum, int begin) {
        if(sum > target) {
            return;
        }
        if(sum == target) {
            result.push_back(combination);
            return;
        }
        for(int i = begin; i < candidates.size(); i++) {
            combination.push_back(candidates[i]);
            combinationSum(result, candidates, combination, target, sum + candidates[i], i);
            combination.pop_back();
        }
    }
};

Version 3

class Solution {
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        vector<vector<int>> result;
        sort(candidates.begin(), candidates.end());
        vector<int> combination;
        combinationSum(result, candidates, combination, target, 0, 0);
        return result;
    }


private:
    void combinationSum(vector<vector<int>>& result, vector<int>& candidates, vector<int> combination, int& target, int sum, int begin) {
        if(sum > target) {
            return;
        }
        if(sum == target) {
            result.push_back(combination);
            return;
        }
        for(int i = begin; i < candidates.size(); i++) {
            combination.push_back(candidates[i]);
            combinationSum(result, candidates, combination, target, sum + candidates[i], i);
            combination.pop_back();
        }
    }
};