暴力就好了- -leetcode上面的题目就是暴力

class Solution {
    void dfs(vector<int>&v, int p, int target, vector<int> & stk,
        vector<vector<int> > & ans){
            if(target == 0){
                ans.push_back(stk);
                return ;
            }
            if(p >= v.size())
                return ;
            dfs(v, p + 1, target, stk, ans);
            int i = 1;
            for(; i * v[p] <= target; ++ i){
                stk.push_back(v[p]);
                dfs(v, p + 1, target - i * v[p], stk, ans);
            }
            while(-- i > 0)
                stk.pop_back();
        }
public:
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        sort(candidates.begin(), candidates.end());
        
        vector<vector<int> > ans;
        vector<int> stk;
        dfs(candidates, 0, target, stk, ans);
        return ans;
    }
};