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Data Structures
  • Data Structures Manual
  • Arrays
    • Array ADT
    • Linear Search
    • Binary Search
    • Some More Basic Operations
    • Reversing an Array
    • Operations in a Sorted Array
    • Merging Two Arrays
    • Set Operations
    • Finding Missing Elements
    • Duplicates in an Array
    • Getting a Pair whose Sum = K
    • Finding Max & Min in Single Scan
  • Strings
    • Finding the Length of a String
    • Changing Cases in a String
    • Finding Number of Vowels, Consonants & Words
    • Reversing a String
    • Checking for Palindrome
    • Duplicates in a String
    • Checking if Strings are Anagrams
    • Permutations of a String
  • Singly Linked List
    • Displaying the Nodes
    • Counting the Nodes
    • Sum of all Nodes
    • Finding the Maximum Element
    • Searching in a Node
    • Inserting a Node
    • Inserting a Node in Sorted List
    • Deleting a Node
    • Checking if List is Sorted
    • Removing Duplicates from a List
    • Reversing a Linked List
    • Concatenating Two Lists
    • Detecting a Loop in Linked List
    • Merge Two Sorted Lists
    • Finding the Middle Node
  • Cirular Linked List
    • Displaying the Nodes
    • Inserting a Node
    • Deleting a Node
  • Doubly Linked List
    • Inserting a Node
    • Deleting a Node
    • Reversing a Doubly Linked List
    • Circular Doubly Linked List
  • Stack
    • Stack Using Array
    • Stack Using Linked List
    • Balancing Parenthesis
    • Infix to Postfix
    • Evaluation of Postfix Expression
  • Queue
    • Queue using Array
    • Queue using Linked List
    • Double Ended Queue
  • Binary Tree
    • Creating a Binary Tree using Queue
    • Recursive Tree Traversals
    • Iterative Tree Traversals
    • Level Order Traversal
    • Counting Nodes in a Binary Tree
    • Finding the Height of Tree
    • Finding Sum of All Nodes
  • Binary Search Tree
    • Searching in a BST
    • Inserting in a BST
    • Deleting in a BST
  • AVL Tree
    • Inserting in an AVL Tree
    • AVL Tree Rotations
    • Deleting in an AVL Tree
  • Heap
    • Inserting in a Heap
    • Deleting in a Heap
    • Heapify
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  • Finding Duplicates in a Sorted Array:
  • Counting Duplicates in a Sorted Array:
  • Using Hash Array:

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  1. Arrays

Duplicates in an Array

Procedure to find and count duplicates in an array.

Finding Duplicates in a Sorted Array:

void findDuplicates(int a[], int n) {

    int lastDuplicate = 0;
    printf("Duplicates in the array :\n");

    for (int i = 0; i < n; i++) {
        // If two or more same elements appear consecutively
        if (a[i] == a[i+1] && lastDuplicate != a[i]) {
            printf("%d\t", a[i]);
            // Keeping track of latest duplicate to avoid
            // printing the same duplicate again
            lastDuplicate = a[i];
        }
    }
    printf("\n");
    
}

Counting Duplicates in a Sorted Array:

void countDuplicates(int a[], int n) {

    int j;
    printf("Duplicates in the array :\n");

    for (int i = 0; i < n-1; i++) {
        if (a[i] == a[i+1]) {
            // Start counting duplicates from i + 1
            j = i + 1;
            while (a[i] == a[j]) {
                // Finding the number of duplicates
                j++;
            }
            printf("%d is appearing %d times\n", a[i], j-i);
            // Start looking for duplicates again
            i = j - 1; 
        }    
    }

}

Using Hash Array:

void findAndCountDuplicates(int a[], int n, int high) {

    // Creating a hash array and initializing with 0
    // Size of hash array = maximum element in input array
    int h[high];
    for (int i = 0; i < high; i++) {
        h[i] = 0;
    }
    
    // Incrementing hash table values as per the numbers in
    // original input array
    for (int i = 0; i < n; i++) {
        h[a[i]]++;
    }
    
    // If any element in hash table has value > 1,
    // it means that the element is repeated
    for (int i = 0; i <= high; i++) {
        if (h[i] > 1) {
            printf("%d appears %d times\n", i, h[i]);
        }
    }

}

Contributed by Nitin Ranganath

PreviousFinding Missing ElementsNextGetting a Pair whose Sum = K

Last updated 5 years ago

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