Arrays.sort(arr);
        if(arr.length==1)
        return 2;
        int x=arr[arr.length-1];
        int dummy[]=new int[x+1];
        for(Integer z: arr){
           dummy[z]=1;  
        }
        
        int found=-1;
        for(int i=1;i<=x;i++){
            if(dummy[i]==0){
                found= i;
            }
        }
        if(found==-1)
        return x+1;
        else
        return found;
https://www.geeksforgeeks.org/problems/find-duplicates-in-an-array/1
1 min

Vineet Kumar  to  You (direct message) 20:34
ok sir

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

class IntArray {
    public static int[] input(BufferedReader br, int n) throws IOException {
        String[] s = br.readLine().trim().split(" ");
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = Integer.parseInt(s[i]);

        return a;
    }

    public static void print(int[] a) {
        for (int e : a) System.out.print(e + " ");
        System.out.println();
    }

    public static void print(ArrayList<Integer> a) {
        for (int e : a) System.out.print(e + " ");
        System.out.println();
    }
}

class GFG {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int t;
        t = Integer.parseInt(br.readLine());
        while (t-- > 0) {

            int n;
            n = Integer.parseInt(br.readLine());

            int[] arr = IntArray.input(br, n);

            Solution obj = new Solution();
            ArrayList<Integer> res = obj.duplicates(arr);

            IntArray.print(res);
        }
    }
}

// } Driver Code Ends


https://www.geeksforgeeks.org/problems/find-duplicates-in-an-array/1
class Solution {
    public static ArrayList<Integer> duplicates(int[] arr) {
        // code here
        //2 3 1
        HashMap<Integer,Integer> hm=new HashMap<>();
        //put , get , ContainsKey
        //process each and every element
        //check wheather the element present in Map or not
        //if yes get actual freq+1
        //if no just place aginest 1
        
        for(Integer i: arr){
            if(hm.containsKey(i)){
                int actfreq=hm.get(i);
                actfreq++;
                hm.put(i,actfreq);
            }else{
                hm.put(i,1);
            }
        }
        ArrayList<Integer> al=new ArrayList<>();
        for(Map.Entry<Integer,Integer> me: hm.entrySet()){
            if(me.getValue()>1){
                al.add(me.getKey());
            }
        }
        if(al.size()==0)
        {
            al.add(-1);
            return al;
        }
        else{
            Collections.sort(al);
            return al;
        }
    }
}
===========================================================
https://www.geeksforgeeks.org/problems/find-the-frequency/1



//{ Driver Code Starts
//Initial Template for Java

import java.io.*;
import java.util.*;

class FastReader{ 
    BufferedReader br; 
    StringTokenizer st; 

    public FastReader(){ 
        br = new BufferedReader(new InputStreamReader(System.in)); 
    } 

    String next(){ 
        while (st == null || !st.hasMoreElements()){ 
            try{ st = new StringTokenizer(br.readLine()); } catch (IOException  e){ e.printStackTrace(); } 
        } 
        return st.nextToken(); 
    } 

    String nextLine(){ 
        String str = ""; 
        try{ str = br.readLine(); } catch (IOException e) { e.printStackTrace(); } 
        return str; 
    } 
    
    Integer nextInt(){
        return Integer.parseInt(next());
    }
} 
    
class GFG {
    public static void main(String args[]) throws IOException {
        FastReader sc = new FastReader();
        PrintWriter out = new PrintWriter(System.out);
        int t = sc.nextInt();
        while (t-- > 0) {
            Solution ob = new Solution();
            int N = sc.nextInt(), Arr[] = new int[N];
    	    for(int i = 0;i<N;i++){
    	        Arr[i] = sc.nextInt();
    	    }
    	    
    	    // element whose frequency to be find
    	    int X = sc.nextInt();
    	    out.println(ob.findFrequency(Arr, X));
        }
        out.flush();
    }
}

// } Driver Code Ends


//User function Template for Java

class Solution{
    int findFrequency(int arr[], int X){
         HashMap<Integer,Integer> hm=new HashMap<>();
        //put , get , ContainsKey
        //process each and every element
        //check wheather the element present in Map or not
        //if yes get actual freq+1
        //if no just place aginest 1
        
        for(Integer i: arr){
            if(hm.containsKey(i)){
                int actfreq=hm.get(i);
                actfreq++;
                hm.put(i,actfreq);
            }else{
                hm.put(i,1);
            }
        }
        int x=0; 
        for(Map.Entry<Integer,Integer> me: hm.entrySet()){
            if(me.getKey()==X){
               x= me.getValue();
            }
        }
        return x;
    }
}
=============================================
class Solution {
    // Function to return the position of the first repeating element.
    public static int firstRepeated(int[] arr) {
        // Your code here
        HashMap<Integer,Integer> hm=new HashMap<>();
        int x=-1;
        for(int i=arr.length-1;i>=0;i--){
            if(hm.containsKey(arr[i])){
                x=i+1;
            }else{
                hm.put(arr[i],1);
            }
        }
        return x;
    }
}