C Exercises: Remove duplicates from a unsorted singly linked list

Last update on October 16 2025 11:04:07 (UTC/GMT +8 hours)

16. Duplicate Removal Challenges

Write a C program to remove duplicates from a single unsorted linked list.

Sample Solution:

C Code:

#include<stdio.h>
#include <stdlib.h>

// Define a structure for a Node in a singly linked list
struct Node {
    int data;
    struct Node* next;
};

// Function to create a new node with given data
struct Node* newNode(int data) {
    // Allocate memory for a new node
    struct Node* node = (struct Node*) malloc(sizeof(struct Node));
    // Set the data for the new node
    node->data = data;
    // Set the next pointer of the new node to NULL
    node->next = NULL;
    return node;
}

// Function to remove duplicates from a sorted linked list
void remove_Duplicates(struct Node* head) {
    // Declare pointers to traverse the list
    struct Node *current = head, *next_next;

    // Traverse the list until the end is reached
    while (current->next != NULL) {
        // Check if the current node's value is equal to the next node's value
        if (current->data == current->next->data) {
            // Update pointers to remove the duplicate node
            next_next = current->next->next;
            free(current->next); // Free memory of the duplicate node
            current->next = next_next; // Update the link to bypass the duplicate node
        } else {
            current = current->next; // Move to the next node
        }
    }
}

// Function to display the elements of a linked list
void displayList(struct Node* head) {
    // Traverse the list and print each element
    while (head) {
        printf("%d ", head->data);
        head = head->next;
    }
    printf("\n");
}

// Main function where the execution starts
int main() {
    // Create the first linked list
    struct Node* head1 = newNode(1);
    head1->next = newNode(2);
    head1->next->next = newNode(3);
    head1->next->next->next = newNode(3);
    head1->next->next->next->next = newNode(4);

    printf("Original Singly List:\n");
    displayList(head1); // Display the original list

    printf("After removing duplicate elements from the said singly list:\n");
    remove_Duplicates(head1); // Remove duplicates
    displayList(head1); // Display the modified list without duplicates

    // Create the second linked list
    struct Node* head2 = newNode(1);
    head2->next = newNode(2);
    head2->next->next = newNode(3);
    head2->next->next->next = newNode(3);
    head2->next->next->next->next = newNode(4);
    head2->next->next->next->next->next = newNode(4);

    printf("\nOriginal Singly List:\n");
    displayList(head2); // Display the original list

    printf("After removing duplicate elements from the said singly list:\n");
    remove_Duplicates(head2); // Remove duplicates
    displayList(head2); // Display the modified list without duplicates

    return 0; // Indicates successful completion of the program
}

Sample Output:

Original Singly List:
1 2 3 3 4 
After removing duplicate elements from the said singly list:
1 2 3 4 

Original Singly List:
1 2 3 3 4 4 
After removing duplicate elements from the said singly list:
1 2 3 4

Flowchart :

Flowchart: Remove duplicates from a unsorted singly linked list.

For more Practice: Solve these Related Problems:

Write a C program to remove duplicates from an unsorted linked list using a hash table.
Write a C program to remove duplicate nodes from a singly linked list without using extra memory.
Write a C program to remove duplicates only if a node appears more than once in the linked list.
Write a C program to recursively remove duplicate nodes from an unsorted linked list.

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