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

Combination_Sum_III.java

//https://leetcode.com/problems/combination-sum-iii/
public class Solution {
    
    //ans
	public static List<List<Integer>> result = new ArrayList<List<Integer>>();
	
	public static List<List<Integer>> combinationSum3(int k, int n) {
		result.clear();
		List<Integer> curr = new ArrayList<Integer>();
		
		helper(curr, k, 1, n);
		
		return result;
	}

	public static void helper(List<Integer> curr, int k, int start, int sum) {
		if (sum < 0) {
			return;
		}
		if (sum == 0 && curr.size() == k) {
			result.add(new ArrayList<Integer>(curr));
			return;
		}
		for (int i = start; i <= 9; i++) {
			curr.add(i);
			helper(curr, k, i + 1, sum - i);
			curr.remove(curr.size() - 1);
		}
	}
	
}