LeetCode 39. Combination Sum 题解

39. Combination Sum

 

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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.
• 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]
]

解题思路：

本题可采用深度优先搜索的方法，遍历每一种可行解，具体参见代码注释。

代码展示：

class Solution {
public:
    vector> combinationSum(vector& candidates, int target) {
        int csize= candidates.size();
        sort(candidates.begin(),candidates.end());
        sol=candidates;
        vector tmp;
        dfs(tmp,target,0);
        return res;
        
    }
private:
    vector > res;
    vector sol;
    int sum(vector tmp)
    {
        int n = tmp.size();
        int tmp_sum=0;
        for(int i=0;i &tmp,int target, int l)
    {
        if(l==sol.size()) return;//l==size时，所有情况都遍历过
        int tmp_tot = sum(tmp); //计算tmp的和，如果大于target则剪枝，等于target则为一合法解，小于target继续添加数
        if(tmp_tot>target) return ;
        else if(tmp_tot==target)
        {
            res.push_back(tmp);
            return ;
        }
        else
        {
            for(int i=l;i