Combination Sum III

// https://leetcode.com/explore/challenge/card/september-leetcoding-challenge/555/week-2-september-8th-september-14th/3457/\

class Solution {
    void find_combinations(int digits_required, int sum_remaining,int pos,std::vector<int> & c_vec) {
        if(sum_remaining < 0 || digits_required < 0)
            return;

        if(digits_required == 0 && sum_remaining == 0) {
                result.push_back(c_vec);
        } else {
            for(int i = pos; i <= 9; ++i  ) {
                c_vec.emplace_back(i);
                find_combinations(digits_required-1, sum_remaining - i, i+1, c_vec);
                c_vec.pop_back();
            }
        }
    }

    std::vector<std::vector<int>> result;
public:
    vector<vector<int>> combinationSum3(int k, int n) {
        std::vector<int> c_vec;

        find_combinations(k, n, 1, c_vec);
        return result;
    }
};