package medium;

import java.util.*;

public class CombinationSumIII {

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

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

int[] nums = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

helper(k, n, nums, 0, new ArrayList(), result);

return result;

}

void helper(int k, int n, int[] nums, int start, List<Integer> curr, List<List<Integer>> result) {

if (n > 0) {

for (int i = start; i < nums.length; i++) {

curr.add(nums[i]);

helper(k, n - nums[i], nums, i + 1, curr, result);// it needs to be a unique set of

// numbers, so we need to set it

// as i+1 here: each number is

// used only once in this array:

// [1,2,3,4,5,6,7,8,9]

curr.remove(curr.size() - 1);

}

} else if (n == 0 && curr.size() == k) {//this is the major difference here: check size of curr list is of k before adding it

List<Integer> temp = new ArrayList(curr);

result.add(temp);

}

}

}