Java Program to remove duplicate element in an Array

We can remove duplicate element in an array by 2 ways: using temporary array or using separate index. To remove the duplicate element from array, the array must be in sorted order. If array is not sorted, you can sort it by calling Arrays.sort(arr) method.

1) Remove Duplicate Element in Array using Temporary Array

public class RemoveDuplicateInArrayExample{
public static int removeDuplicateElements(int arr[], int n){
        if (n==0 || n==1){
            return n;
        }
        int[] temp = new int[n];
        int j = 0;
        for (int i=0; i<n-1; i++){
            if (arr[i] != arr[i+1]){
                temp[j++] = arr[i];
            }
         }
        temp[j++] = arr[n-1];   
        // Changing original array
        for (int i=0; i<j; i++){
            arr[i] = temp[i];
        }
        return j;
    }
     
    public static void main (String[] args) {
        int arr[] = {10,20,20,30,30,40,50,50};
        int length = arr.length;
        length = removeDuplicateElements(arr, length);
        //printing array elements
        for (int i=0; i<length; i++)
           System.out.print(arr[i]+" ");
    }
}

Test it Now

Output:

10 20 30 40 50

2) Remove Duplicate Element in Array using separate index

public class RemoveDuplicateInArrayExample2{
    public static int removeDuplicateElements(int arr[], int n){
        if (n==0 || n==1){
            return n;
        }  
        int j = 0;//for next element
        for (int i=0; i < n-1; i++){
            if (arr[i] != arr[i+1]){
                arr[j++] = arr[i];
            }
        }
        arr[j++] = arr[n-1];
        return j;
    }
     
    public static void main (String[] args) {
        int arr[] = {10,20,20,30,30,40,50,50};
        int length = arr.length;
        length = removeDuplicateElements(arr, length);
        //printing array elements
        for (int i=0; i<length; i++)
           System.out.print(arr[i]+" ");
    }
}

Test it Now

Output:

10 20 30 40 50

Remove Duplicate Elements in Unsorted Array

If you have unsorted array, you need to sort it first. To do so, use Arrays.sort(arr) method.

import java.util.Arrays;
public class RemoveDuplicateInArrayExample3{
public static int removeDuplicateElements(int arr[], int n){
        if (n==0 || n==1){
            return n;
        }
        int[] temp = new int[n];
        int j = 0;
        for (int i=0; i<n-1; i++){
            if (arr[i] != arr[i+1]){
                temp[j++] = arr[i];
            }
         }
        temp[j++] = arr[n-1];   
        // Changing original array
        for (int i=0; i<j; i++){
            arr[i] = temp[i];
        }
        return j;
    }
     
    public static void main (String[] args) {
        int arr[] = {10,70,30,90,20,20,30,40,70,50};//unsorted array
        Arrays.sort(arr);//sorting array
        int length = arr.length;
        length = removeDuplicateElements(arr, length);
        //printing array elements
        for (int i=0; i<length; i++)
           System.out.print(arr[i]+" ");
    }
}

Test it Now

Output: