LeetCode 39. Combination Sum

Combination Sum

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题目描述:

Given a set of candidate numbers (C) (without duplicates) 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.
• 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]]

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题目大意:

给定一个数组candidates和一个数字target，挑选candidates中元素，使这些元素的和等于target。其中的元素可以用多次。
dfs遍历所有的情况，注意控制边界即可。

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题目代码:

class Solution {public:    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {        dfs(0, 0, candidates, target);        return ans;    }private:    vector<vector<int>>ans;    vector<int>elements;    void dfs(int cur, int sum, vector<int>&candidates, int target){                if(sum > target)            return ;        if(sum == target){            ans.push_back(elements);            return ;        }                for(int i = cur; i < candidates.size(); i++){            elements.push_back(candidates[i]);            dfs(i, sum+candidates[i], candidates, target);            elements.pop_back();        }            }};