Number of score combinations, dynamic programming help, ( from elements of programming interviews, java)

Given scores for individual plays and a final target score, the objective is to compute the number of possible combinations. (for example, if the target score is 6 and play scores are <1,3>, there are 3 ways to reach the target score - 3x2, 3x1 + 1x3, 1x6)

I can't see why my code is wrong:

import java.util.*;
public class Main
{
    public static int combinations(int target, List<Integer> plays) {
        Collections.sort(plays);
        HashMap<Integer, Integer> map = new HashMap<>(); //map score to combinations. 
        map.put(0,1);
        combHelper(target,plays,plays.size() -1, map);
        return map.get(target);
        
    }
    
    private static int combHelper(int target, List<Integer> plays, int i, HashMap<Integer, Integer> map) {
        if (target < 0 || i < 0) {
            return 0;
        }
        if (!map.containsKey(target)) {
            int out = combHelper(target,plays,i - 1, map) + combHelper(target - plays.get(i),plays,i,map);
            map.put(target,out);
        }
        return map.get(target);
    }
    
	public static void main(String[] args) {
	    List<Integer> points = new ArrayList<>(Arrays.asList(3,1));
		System.out.println(combinations(6,points)); //output is 2
	}
}

any help and feedback would be appreciated!

I don't know what is wrong with your code, but it looks difficult to understand.

There is a simpler & easier we to solve this without recursion.

Steps:

• create an array dp with size target + 1
• for each point in points update dp

import java.util.List;
import java.util.Arrays;

public class Main
{   
    static int noOfWays(List<Integer> points, int target) {
        
        int[] dp = new int[target + 1];
        dp[0] = 1;
        for(int point: points)
            for(int i = point; i <= target; i++)
                dp[i] += dp[i - point];

        return dp[target];
    }

    public static void main(String[] args) {
        List<Integer> points = Arrays.asList(1, 3);
        int target = 6;
        System.out.println(noOfWays(points, target));
    }
}