leetcode.39 --- 组合总和

题解：

代码如下：

class Solution {
public:
    vector> ans;
    vector path;
    vector> combinationSum(vector& candidates, int target) {
        dfs(candidates,0,target);
        return ans;
    }
    void dfs(vector&a,int u,int target)
    {
        if(target < 0) return; //不满足
        if(target == 0){  //该方案合法，记录到path中
            ans.push_back(path);
            return;
        }
        for(int i = u;i < a.size();i++)
        {
            if(a[i] <= target){
                path.push_back(a[i]);
                dfs(a,i,target - a[i]); //用target - a[i]来算，减到0就可以
                path.pop_back(); //恢复
            }
        }
    }
};