Duplicate Elements: Find duplicates in an array

This program demonstrates how to find duplicate elements in an array using Java. The algorithm iterates through the array and uses a HashSet to track seen elements. If an element is found in the HashSet, it is identified as a duplicate.

Java Program

import java.util.HashSet;

public class DuplicateElements {
    /**
     * Finds and prints duplicate elements in the given array.
     *
     * @param array The array to check for duplicates.
     */
    public static void findDuplicates(int[] array) {
        HashSet<Integer> seen = new HashSet<>();
        HashSet<Integer> duplicates = new HashSet<>();
        
        for (int element : array) {
            if (!seen.add(element)) {
                duplicates.add(element);
            }
        }
        
        if (duplicates.isEmpty()) {
            System.out.println("No duplicates found.");
        } else {
            System.out.println("Duplicate elements: " + duplicates);
        }
    }

    public static void main(String[] args) {
        int[] array = {1, 2, 3, 4, 5, 6, 7, 2, 3, 8, 9, 10, 10};
        findDuplicates(array);
    }
}

Explanation

The program includes the following components:

• import java.util.HashSet;: Imports the HashSet class from the Java Collections Framework.
• public class DuplicateElements: Defines the main class.
• public static void findDuplicates(int[] array): Defines a static method that takes an array of integers as input and prints the duplicate elements.
• HashSet<Integer> seen = new HashSet<>();: Initializes a HashSet to keep track of elements that have been encountered in the array.
• HashSet<Integer> duplicates = new HashSet<>();: Initializes a HashSet to store duplicate elements.
• for (int element : array): Iterates through each element in the array.
• if (!seen.add(element)): Checks if the element can be added to the seen set. If it returns false, it means the element is a duplicate.
• duplicates.add(element): Adds the duplicate element to the duplicates set.
• if (duplicates.isEmpty()): Checks if the duplicates set is empty and prints an appropriate message.
• public static void main(String[] args): The main method that initializes an array and calls the findDuplicates method.

The example array int[] array = {1, 2, 3, 4, 5, 6, 7, 2, 3, 8, 9, 10, 10}; contains the duplicates 2, 3, and 10. When the findDuplicates method is called, it will print:

No duplicates found.
Duplicate elements: [2, 3, 10]

Explanation

• Java Program: The provided Java program utilizes the HashSet class to identify duplicate elements in an array. The findDuplicates method iterates through the array, adding each element to a HashSet called seen. If an element cannot be added (because it is already in the seen set), it is added to a HashSet called duplicates.
• Output: The output of the program will list all the duplicate elements found in the array.