https://www.geeksforgeeks.org/problems/intersection-of-two-arrays2404/1?utm_source=geeksforgeeks&utm_medium=ml_article_practice_tab&utm_campaign=article_practice_tab


//{ Driver Code Starts
import java.io.*;
import java.util.*;

class GFG {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int t = Integer.parseInt(br.readLine().trim());
        while (t-- > 0) {
            // First array input
            String[] str1 = br.readLine().trim().split(
                " "); // Read the first line and split by spaces
            int n = str1.length;
            int[] a = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = Integer.parseInt(str1[i]); // Convert each element to an integer
            }

            // Second array input
            String[] str2 = br.readLine().trim().split(
                " "); // Read the second line and split by spaces
            int m = str2.length;
            int[] b = new int[m];
            for (int i = 0; i < m; i++) {
                b[i] = Integer.parseInt(str2[i]); // Convert each element to an integer
            }

            Solution sln = new Solution();
            System.out.println(sln.numberofElementsInIntersection(a, b));
        }
    }
}

// } Driver Code Ends


class Solution {
    public static int numberofElementsInIntersection(int a[], int b[]) {
        // Your code here
        
        HashSet<Integer> al=new HashSet<>();
        for(Integer i:a){
            al.add(i);
        }
        int count=0;
        for(Integer i:b){
            if(al.contains(i)){
               count++; 
            }
        }
        return count;
    }
}
=================================================================

       int maxlen=0;
        HashMap<Integer,Integer> hm=new HashMap<>();
        int sum=0;
        int n=arr.length;
        for(int i=0;i<n;i++){
            sum=sum+arr[i];
            if(sum==k){
                if(i+1>maxlen){
                    maxlen=i+1;
                }
            }
            if(hm.containsKey(sum-k)){
                int len=i-hm.get(sum-k);
                if(len>maxlen){
                    maxlen=len;
                }
            }

            if(!hm.containsKey(sum)){
                hm.put(sum,i);
            }
        }
        return maxlen;
========================================

k=4

1 2 1 0 1

sum=1
sum=1+2=3
sum= 3+1=4

 int max=Integer.MIN_VALUE;
        boolean found=false;
        for(int i=0;i<arr.length;i++){
            int sum=0;
            for(int j=i;j<arr.length;j++){
                sum=sum+arr[j];
                if(sum==k){
                    found=true;
                    int cmax=j-i+1;
                    if(cmax>max){
                        max=cmax;
                    }

                }
            }
        }
        if(found==false)
        return 0;
        else
        return max;
=============================================