Getting an error while implementing memoization in the java code

Question

Memoization is giving me wrong answers. Please can some one help me out here. Without memorization, I am getting the right answers as in function targetBestR, but in the memoized function targetBestM, I am getting the wrong values being stored in the array list for the respective keys.

import java.util.ArrayList;

import java.util.HashMap;

public class TargetSumBest {

public static ArrayList<Integer> targetBestR(int n, int arr[]){
    if(n==0) return new ArrayList<Integer>();
    if(n<0) return null;
    ArrayList<Integer> shortestCombo=null;
    for(int i=0;i<arr.length;i++) {
        //System.out.println(i);
        //System.out.println(arr[i]);
        int rem=n-arr[i];
        //System.out.println(n+"-"+i+"="+rem);
        ArrayList<Integer> tar=targetBestR(rem, arr);
        if(tar!=null) {
            tar.add(arr[i]);
            if(shortestCombo==null||tar.size()<shortestCombo.size()) {
                shortestCombo=tar;
            }
        }
    }
    //System.out.println(n+"value"+shortestCombo);
    return shortestCombo;
}   
public static ArrayList<Integer> targetBestM(int n, int arr[], HashMap<Integer, ArrayList<Integer>> memo){
    if(n==0) return new ArrayList<Integer>();
    if(n<0) return null;
    if(memo.containsKey(n)) return memo.get(n);
    ArrayList<Integer> shortestCombo=null;
    for(int i=0;i<arr.length;i++) {
        //System.out.println(i);
        //System.out.println(arr[i]);
        int rem=n-arr[i];
        //System.out.println(n+"-"+i+"="+rem);
        ArrayList<Integer> tar=targetBestM(rem, arr,memo);
        if(tar!=null) {
            tar.add(arr[i]);
            if(shortestCombo==null||tar.size()<shortestCombo.size()) {
                shortestCombo=tar;
                
            }
        }
    }
    //System.out.println(n+"value"+shortestCombo);
    memo.put(n, shortestCombo);
    return shortestCombo;
}   
public static void main(String[] args) {
    int n=8; int arr[]= {1,4,2};
    
    System.out.println(targetBestM(n, arr, new HashMap<Integer, ArrayList<Integer>>()));
    System.out.println(targetBestR(n, arr));
}
}//error

Answer 1

Was able to find the problem. The array passed into the HashMap keeps getting used and added to. Was able to fix it by creating new ArrayLists when reading and writing from the HashMap.

when reading...

    if (memo.containsKey(n)) {
        System.out.println(indent + n +  " memo.get(n) = " + memo.get(n));
        return new ArrayList<>(memo.get(n));
    }

when writing...

    memo.put(n, new ArrayList<>(shortestCombo));