public List<List<Integer>> combinationSum3(int k, int n) {

        int[] candidate = new int[9];
        for (int i = 0; i < 9; ++i) {
            candidate[i] = i + 1;
        }
        List<Integer> temp = new ArrayList<Integer>();
        dfs(candidate, temp, 0, n, 0, k);
        return res;

    }