Count Coins - JAVA

// Author : Saurav Kalsoor
// Count Coins- JAVA

import java.util.*;

public class Test {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {

        int n = sc.nextInt();
        int m = sc.nextInt();

        ArrayList<Integer> coins = new ArrayList<>();
        for(int i =0; i < n; i++){
            coins.add(sc.nextInt());
        }

        ArrayList<Edge> arr = new ArrayList<>();
        for(int i=0; i < m; i++){
            int u = sc.nextInt();
            int v = sc.nextInt();

            arr.add(new Edge(u, v));
        }

        System.out.println(coinsCount(arr, coins, n));
    }

    public static int coinsCount(ArrayList<Edge> arr, ArrayList<Integer> coins, int n) {
        ArrayList<ArrayList<Integer>> tree = new ArrayList<>();
        for(int i = 0; i < n; i++) tree.add(new ArrayList<>());
        for(Edge e : arr){
            tree.get(e.u).add(e.v);
            tree.get(e.v).add(e.u);
        }
        HashMap<Integer, Integer> mp = new HashMap<>();
        return uniqueCount(tree, mp, coins, 0, -1);
    }

    public static int uniqueCount(ArrayList<ArrayList<Integer>> tree, HashMap<Integer, Integer> mp, ArrayList<Integer> coins, int node, int parent){

        int res = 0;
        mp.put(coins.get(node), mp.getOrDefault(coins.get(node), 0) + 1);
        for(int child : tree.get(node)){
            if(child == parent) continue;

            res = Math.max(res, uniqueCount(tree, mp, coins, child, node));
        }

        res = Math.max(res, mp.size());
        mp.put(coins.get(node), mp.get(coins.get(node)) - 1);
        if(mp.get(coins.get(node)) == 0)
            mp.remove(coins.get(node));
        return res;
    }

}

class Edge{
    int u, v;
    Edge(int u, int v){
        this.u = u;
        this.v = v;
    }
}