public List<List<Integer>> combinationSum3(int k, int n) {
		if (k == 0 || n <= 0)
			return result;
		if (n > 45)
			return result;
		int[] nums = new int[9];
		for (int i = 0; i < 9; i++) {
			nums[i] = i + 1;
		}
		backtrack(nums, k, n, 0, 0, 0);
		return result;
	}