LeetCode 216 组合总和 III

class Solution {
public:
    vector<vector<int>> res;
    vector<int> path;
    int sum = 0;
    

    void dfs(int start, int k, int n) {
        if (path.size() > k || sum > n) return;

        if (path.size() == k && sum == n) {
            res.push_back(path);
            return;
        }

        for (int i = start; i <= 9; i ++) {
            path.push_back(i);
            sum += i;
            dfs(i + 1, k, n);
            path.pop_back();
            sum -= i;
        }
    }

    vector<vector<int>> combinationSum3(int k, int n) {
        dfs(1, k, n);

        return res;
    }
};