39. Combination Sum

1刷
暴力递归，一开始是想不出来的，以为是数据结构，听说dp也可以解， 昊哥提醒了才想出，其实应该挺容易 的，只是我死活觉得暴力会超时。。。。Acm的后患。。。

class Solution {
public:
    void getit(int target, int sum, int num, vector<int>& cand, vector<int>& now, vector<vector<int>>& ll){
     if(sum == target){
         ll.push_back(now);
         return;
     }   
     if(sum > target) return;

     for(int i = num; i < cand.size(); ++ i){
         sum += cand[i];
         now.push_back(cand[i]);
         getit(target, sum, i, cand, now, ll);
         now.pop_back();
         sum -= cand[i];
     }
     return;
    }

    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
     sort(candidates.begin(), candidates.end());
     vector<vector<int>> last;
     vector<int> now;
     getit(target, 0, 0, candidates, now, last);
     return last;
    }
};

2刷
是dfs，但是就是要怎样才能写好代码！！！！发现1刷的时候竟然写出来了，伤心！
3刷要看剪子！！！！

class Solution {
public:
    vector<vector<int>>ve;
    void findit(vector<int>& cand, vector<int> & vec, int target, int begin){
        if(target == 0){
            ve.push_back(vec);
            return ;
        }
        for(int i = begin; i < cand.size() && target >= cand[i]; ++ i){
            vec.push_back(cand[i]);
            findit(cand, vec, target - cand[i], i);
            vec.pop_back();
        }

    }
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        sort(candidates.begin(), candidates.end());
        vector<int>vec;
        findit(candidates, vec, target, 0);
        return ve;
    }
};