Java Program to Remove Duplicate Elements from Array

This is the Java Program to Remove Duplicates in a Sorted Array.

Problem Description

Given a sorted array of integers, remove the duplicates of the elements from the array.
Example:

Array = [1 2 2 3 3 4]

Output
Array = [1 2 3 4]

Problem Solution

Traverse the array from beginning to end and in a variable, an index, where the element having a duplicate will be copied. The idea is to copy each unique element to the beginning of the array and print that part of the array.

Program/Source Code

Here is the source code of the Java Program to Remove Duplicates in a Sorted Array. The program is successfully compiled and tested using IDE IntelliJ Idea in Windows 7. The program output is also shown below.

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//Java Program to Remove Duplicates in a Sorted Array

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import java.io.BufferedReader;
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import java.io.InputStreamReader;
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public class RemoveDuplicates {
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    // Function to remove the duplicates

    static int removeDuplicates(int[] array){

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        int replaceIndex = 0;
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        int i,j;
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        for(i=0; i<array.length; i++){
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            for(j=i+1; j<array.length; j++){

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                if(array[j]!=array[i]){
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                    break;
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                }
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            }
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            array[replaceIndex++] = array[i];

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            i = j-1;
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        }
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        return replaceIndex;
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    }
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    // Function to read user input
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    public static void main(String[] args) {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

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        int size;
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        System.out.println("Enter the size of the array");

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        try {
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            size = Integer.parseInt(br.readLine());

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        } catch (Exception e) {
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            System.out.println("Invalid Input");

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            return;
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        }
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        int[] array = new int[size];
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        System.out.println("Enter array elements in sorted order");

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        int i;
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        for (i = 0; i < array.length; i++) {

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            try {
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                array[i] = Integer.parseInt(br.readLine());

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            } catch (Exception e) {
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                System.out.println("An error occurred");

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                return;
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            }
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        }
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        int index = removeDuplicates(array);

        System.out.println("Array after removing duplicates is");

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        for(i=0; i<index; i++){
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            System.out.print(array[i] + " ");

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        }
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    }
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}
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Program Explanation

1. In function removeDuplicates(), we declare and initialize variable replaceIndex to 0.
2. The loop for(i=0; i<array.length; i++) is used to iterate through the array.
3. The nested loop for(j=i+1; j<array.length; j++) is used to check for duplicate elements, it breaks out of the loop if the condition if(array[j]!=array[i]) is true.
4. Finally, array[i] is copied to position replaceindex and i is set to j-1, to avoid scanning again through duplicate elements.

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Time Complexity: O(n) where n is the number of elements in the array.

Runtime Test Cases

 
Case 1 (Positive Test Case - Involving Duplicates):
 
Enter the size of the array
6
Enter array elements in sorted order
1
2
2
3
3
4
Array after removing duplicates is
1 2 3 4
 
Case 2 (Negative test Case - Without Duplicates):
 
Enter the size of the array
4
Enter array elements in sorted order
4
3
2
1
Array after removing duplicates is
4 3 2 1
 
Case 3 (Positive Test Case - Another Example):
 
Enter the size of the array
7
Enter array elements in sorted order
1
3
3
3
4
5
6
Array after removing duplicates is
1 3 4 5 6

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