216 combination sum III

https://leetcode.com/problems/combination-sum-iii/submissions/

class Solution {
    List<List<Integer>> ans = new ArrayList<>();
    public List<List<Integer>> combinationSum3(int k, int n) {
        dfs(k, n, 1, new ArrayList<>());
        return ans;
    }
    private void dfs(int k, int sum, int cur, List<Integer> path) {
        if (sum == 0) {
            if (k == 0 && cur <= 10) {
                ans.add(new ArrayList<>(path));
            }
            return;
        }
        if (k <= 0 || sum < 0 || cur >= 10) {
            return;
        }
        dfs(k, sum, cur + 1, path);
        path.add(cur);
        dfs(k - 1, sum - cur, cur + 1, path);
        path.remove(path.size() - 1);
    }
}

终止条件太多了有点tricky