Remove duplicate from an Array - using hset and in Place

removeDuplicate.java

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

class removeDuplicate
{
    public static void main (String[] args)
    {
        removeDuplicate obj = new removeDuplicate();
        obj.approachTwo();
        obj.approachOne();
    }
    
    public void approachTwo()
    {
        // this approach requires the array to be sorted. for this eg code we are taking a sorted array
        int[] a = new int[]{1, 1, 1, 2, 2, 2, 3, 4, 4, 5, 5};
        int i = 1, j = 0, length = a.length;
        while(i < length) {
            if(a[i] == a[j]) {
                i++;
            } else {
                j++;
                a[j] = a[i];
                i++;
            }
        }
        System.out.println("Array after removing duplicate approach two :");
        for(int k =0; k < j+1; k++) {
           System.out.println(a[k]);
        }
    }
    
    public void approachOne()
    {
        int[] a = new int[]{1, 1, 1, 2, 2, 2, 3, 4, 4, 5, 5};
        Set<Integer> s = new HashSet<Integer>();
        // since we are not sure what will be the size of the new array after removing duplciate we use ArrayList
        List<Integer> b = new ArrayList<Integer>();
        
        for(int value:a) {
            if(s.contains(value)) {
                continue;
            }
            s.add(value);
            b.add(value);
        }
        
        System.out.println("Array after removing duplicate approach one:");
        for(int value:b) {
           System.out.println(value);
        }
    }
}