Sort an array of 0's 1's 2's 3 pointer approach, Java

Sort an array of 0's 1's 2's 3 pointer approach

//'main' method must be in a class 'Rextester'.
//openjdk version '11.0.5' 
import java.io.*;
import java.util.*;
import java.lang.*;

class Rextester
{  
    public static void main(String args[]) throws IOException
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            int n = Integer.parseInt(br.readLine());
            int[] arr = new int[n];
            
            StringTokenizer st = new StringTokenizer(br.readLine());
            for(int i=0;i<n;i++){
                //if(st.hasMoreToken())
                  arr[i] = Integer.parseInt(st.nextToken());
            }
     
        int left = 0;
        int rt = arr.length-1;
        int i = 0;
        while(i<=rt){
            if(arr[i] == 0){
                int temp = arr[i];
                arr[i] = arr[left];
                arr[left] = temp;
                left++;
                i++;
            }
            else if(arr[i] == 2){
                int temp = arr[i];
                arr[i] = arr[rt];
                arr[rt] = temp;
                rt--;
            }
            else if(arr[i] == 1)
                i++;
            
        }
        for(int j=0;j<arr.length;j++)
            System.out.print(arr[j]+" ");
    }
}


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