How to find the duplicate elements in java array ?

To find duplicate elements in an array in Java, you can use various approaches. Here are a few commonly used methods:

1. Using Brute Force: You can use a nested loop to compare each element of the array with all other elements and check for duplicates. If a duplicate is found, you can store or print the element.

   java
   int[] array = {1, 2, 3, 4, 2, 5, 1};
   for (int i = 0; i < array.length - 1; i++) {
       for (int j = i + 1; j < array.length; j++) {
           if (array[i] == array[j]) {
               System.out.println("Duplicate element: " + array[i]);
           }
       }
   }
   

2. Using HashSet: You can utilize a HashSet to keep track of unique elements encountered in the array. When adding elements to the HashSet, if an element is already present, it indicates a duplicate.

   java
   int[] array = {1, 2, 3, 4, 2, 5, 1};
   Set<Integer> uniqueElements = new HashSet<>();
   Set<Integer> duplicateElements = new HashSet<>();
   
   for (int num : array) {
       if (!uniqueElements.add(num)) {
           duplicateElements.add(num);
       }
   }
   
   System.out.println("Duplicate elements: " + duplicateElements);
   

3. Using HashMap: You can utilize a HashMap to store the frequency of each element in the array. If the frequency exceeds 1, it indicates a duplicate element.

   java
   int[] array = {1, 2, 3, 4, 2, 5, 1};
   Map<Integer, Integer> elementFrequency = new HashMap<>();
   
   for (int num : array) {
       elementFrequency.put(num, elementFrequency.getOrDefault(num, 0) + 1);
   }
   
   for (Map.Entry<Integer, Integer> entry : elementFrequency.entrySet()) {
       if (entry.getValue() > 1) {
           System.out.println("Duplicate element: " + entry.getKey());
       }
   }
   

These are a few approaches to find duplicate elements in an array in Java. Choose the one that suits your requirements and the size of the array.