216. Combination Sum III

[namespace-io]

class Solution {
public:
    void comb(int k, int c, int n, int d, vector<int>& p, vector<vector<int>>& ret){
        
        if(c == k) {
            if(n == 0) ret.push_back(p);
            return;
        }
        
        if(d == 10 || n < 0) return;
        
        for(int i = d; i < 10; i++){
            p.push_back(i);
            comb(k, c+1, n - i, i+1, p, ret);
            p.pop_back();
        }
        
    }
    vector<vector<int>> combinationSum3(int k, int n) {
        vector<vector<int>> ret;
        vector<int> p;
        comb(k, 0, n, 1, p, ret);
        return ret;
    }
};