leetcode216组合总和 III

class Solution {
    
    

    List<List<Integer>> res = new ArrayList<>();

    public List<List<Integer>> combinationSum3(int k, int n) {
    
    
        List<Integer> path = new ArrayList<>();
        backtrack(1, k, n, path);
        return res;
    }

    private void backtrack(int id, int k, int n, List<Integer> path){
    
    
        if (n == 0 && k == 0){
    
    
            res.add(new ArrayList<>(path));
            return;
        }
        if (n < 0 && k == 0){
    
    
            return;
        }

        for (int i = id; i < 10; i++) {
    
    

            if (i > n) continue;
            
            n -= i;
            path.add(i);
            backtrack(i + 1, k - 1, n, path);
            path.remove(path.size() - 1);
            n += i;
        }
    }
}