C program to remove duplicate nodes from the singly linked list

In this tutorial, we will learn how to remove duplicate nodes from the singly linked list using the C program? By Nidhi Last updated : August 02, 2023

Problem statement

Given a singly linked list, and we have to remove the duplicate nodes from the linked list.

C program to remove duplicate nodes from the singly linked list

The source code to remove duplicate nodes from the singly linked list is given below. The given program is compiled and executed using GCC compile on UBUNTU 18.04 OS successfully.

// C program to remove duplicate nodes from
// the singly linked list

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

//Self-referential structure to create the node.
typedef struct tmp {
    int item;
    struct tmp* next;
} Node;

//structure for creating the linked list.
typedef struct
    {
    Node* head;
    Node* tail;

} List;

//Initialize List
void initList(List* lp)
{
    lp->head = NULL;
    lp->tail = NULL;
}

//Create node and return the reference of it.
Node* createNode(int item)
{
    Node* nNode;

    nNode = (Node*)malloc(sizeof(Node));

    nNode->item = item;
    nNode->next = NULL;

    return nNode;
}

//Add a new item at the end of the list.
void addAtTail(List* lp, int item)
{
    Node* node;
    node = createNode(item);

    //if list is empty.
    if (lp->head == NULL) {
        lp->head = node;
        lp->tail = node;
    }
    else {
        lp->tail->next = node;
        lp->tail = lp->tail->next;
    }
}

//Add a new item at beginning of the list.
void addAtHead(List* lp, int item)
{
    Node* node;
    node = createNode(item);

    //if list is empty.
    if (lp->head == NULL) {
        lp->head = node;
        lp->tail = node;
    }
    else {
        node->next = lp->head;
        lp->head = node;
    }
}

//To print the list from start to end of the list.
void printList(List* lp)
{
    Node* node;

    if (lp->head == NULL) {
        printf("\nEmpty List");
        return;
    }

    node = lp->head;

    while (node != NULL) {
        printf("| %05d |", node->item);
        node = node->next;

        if (node != NULL)
            printf("--->");
    }
    printf("\n\n");
}

void dupDelete(List* lp)
{
    Node* current = lp->head;
    Node* index;
    Node* temp;

    while (current != NULL) {
        temp = current;

        index = current->next;

        while (index != NULL) {
            if (current->item == index->item)
                temp->next = index->next;
            else
                temp = index;
            index = index->next;
        }
        current = current->next;
    }
}

//Main function to execute program.
int main()
{
    List* lp;

    lp = (List*)malloc(sizeof(List));

    initList(lp);

    addAtTail(lp, 101);
    addAtTail(lp, 102);
    addAtTail(lp, 101);
    addAtTail(lp, 102);
    addAtTail(lp, 105);

    printf("List:\n");
    printList(lp);
    dupDelete(lp);

    printf("Updated List:\n");
    printList(lp);

    return 0;
}

Output

List:
| 00101 |--->| 00102 |--->| 00101 |--->| 00102 |--->| 00105 |

Updated List:
| 00101 |--->| 00102 |--->| 00105 |

Explanation

Here, we created a self-referential structure to implement a linked list, a function to add a node at the start and end of the list, and a function dupDelete() to remove duplicate elements.

In the main() function, we created a singly linked list and called the function dupDelete() to remove the duplicate elements. After that, we printed the updated list.