Leetcode-Complete-Guide/code/216.txt at master · JunBinLiang/Leetcode-Complete-Guide · GitHub

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class Solution {
public:
    unordered_set<int>hash;
    int k,n;
    vector<vector<int>>res;
    vector<vector<int>> combinationSum3(int k, int n) {
        this->k=k;
        this->n=n;

        vector<int>cur;
        dfs(cur,0,0);
        return res;
    }

    void dfs(vector<int>&cur,int sum,int state){
        if(sum>n)return;
        if(cur.size()==k){
            if(sum==n){
                if(hash.find(state)==hash.end()){
                    res.push_back(cur);
                    hash.insert(state);

                }
            }
            return;
        }

        for(int i=1;i<=9;i++){
            if((state&(1<<i))!=0)continue;
            cur.push_back(i);
            dfs(cur,sum+i,state|(1<<i));
            cur.pop_back();
        }

    }
};