C program to delete middle node of Singly Linked List

Write a C program to create a singly linked list of n nodes and delete node from the middle of the linked list. How to delete node from the middle of the singly linked list in C.

Singly linked list

Required knowledge

Basic C programming, Singly linked list, Dynamic memory allocation

Algorithm to delete middle node of Singly Linked List

Algorithm to delete middle node of Singly Linked List
%%Input : head node of the linked list
        n node to be deleted
Begin:
    If (head == NULL) then
        write ('List is already empty')
    End if
    Else then
        toDeletehead
        prevNodehead
        For i←2 to n do
            prevNodetoDelete
            toDeletetoDelete.next
            If (toDelete == NULL) then
                break
            End if
        End for
        If (toDelete != NULL) then
            If (toDelete == head) then
                headhead.next
            End if
            prevNode.nexttoDelete.next
            toDelete.nextNULL
            unalloc (toDelete)
        End if
    End else
End

Steps to delete middle node of Singly Linked List

  1. Traverse to the nth node of the singly linked list and also keep reference of n-1th node in some temp variable say prevnode.
    Deletion of node from middle of singly linked list

  2. Reconnect the n-1th node with the n+1th node i.e. prevNode->next = toDelete->next (Where prevNode is n-1th node and toDelete node is the nth node and toDelete->next is the n+1th node).
    Deletion of node from the middle of singly linked list

  3. Free the memory occupied by the nth node i.e. toDelete node.
    Deletion of node from middle of singly linked list


Program to delete middle node of Singly Linked List

/**
 * C program to delete middle node of Singly Linked List
 */

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


/* Structure of a node */
struct node {
    int data; //Data part
    struct node *next; //Address part
}*head;



void createList(int n);
void deleteMiddleNode(int position);
void displayList();



int main()
{
    int n, position;

    /*
     * Creates a singly linked list of n nodes
     */
    printf("Enter the total number of nodes: ");
    scanf("%d", &n);
    createList(n);

    printf("\nData in the list \n");
    displayList();

    printf("\nEnter the node position you want to delete: ");
    scanf("%d", &position);

    /* Deletes the middle node from list */
    deleteMiddleNode(position);

    printf("\nData in the list \n");
    displayList();

    return 0;
}



/*
 * Create a list of n nodes
 */
void createList(int n)
{
    struct node *newNode, *temp;
    int data, i;

    head = (struct node *)malloc(sizeof(struct node));

    /*
     * If unable to allocate memory for head node
     */
    if(head == NULL)
    {
        printf("Unable to allocate memory.");
    }
    else
    {
        /*
         * Reads data of node from the user
         */
        printf("Enter the data of node 1: ");
        scanf("%d", &data);

        head->data = data; //Links the data field with data
        head->next = NULL; //Links the address field to NULL

        temp = head;

        /*
         * Creates n nodes and adds to linked list
         */
        for(i=2; i<=n; i++)
        {
            newNode = (struct node *)malloc(sizeof(struct node));

            /* If memory is not allocated for newNode */
            if(newNode == NULL)
            {
                printf("Unable to allocate memory.");
                break;
            }
            else
            {
                printf("Enter the data of node %d: ", i);
                scanf("%d", &data);

                newNode->data = data; //Links the data field of newNode with data
                newNode->next = NULL; //Links the address field of newNode with NULL

                temp->next = newNode; //Links previous node i.e. temp to the newNode
                temp = temp->next;
            }
        }

        printf("SINGLY LINKED LIST CREATED SUCCESSFULLY\n");
    }
}



/*
 * Deletes the middle node of the linked list
 */
void deleteMiddleNode(int position)
{
    int i;
    struct node *toDelete, *prevNode;

    if(head == NULL)
    {
        printf("List is already empty.");
    }
    else
    {
        toDelete = head;
        prevNode = head;

        for(i=2; i<=position; i++)
        {
            prevNode = toDelete;
            toDelete = toDelete->next;

            if(toDelete == NULL)
                break;
        }

        if(toDelete != NULL)
        {
            if(toDelete == head)
                head = head->next;

            prevNode->next = toDelete->next;
            toDelete->next = NULL;

            /* Deletes the n node */
            free(toDelete);

            printf("SUCCESSFULLY DELETED NODE FROM MIDDLE OF LIST\n");
        }
        else
        {
            printf("Invalid position unable to delete.");
        }
    }
}



/*
 * Displays the entire list
 */
void displayList()
{
    struct node *temp;

    /*
     * If the list is empty i.e. head = NULL
     */
    if(head == NULL)
    {
        printf("List is empty.");
    }
    else
    {
        temp = head;
        while(temp != NULL)
        {
            printf("Data = %d\n", temp->data); //Prints the data of current node
            temp = temp->next; //Advances the position of current node
        }
    }
} 

Output
Enter the total number of nodes: 5
Enter the data of node 1: 10
Enter the data of node 2: 20
Enter the data of node 3: 30
Enter the data of node 4: 40
Enter the data of node 5: 50
SINGLY LINKED LIST CREATED SUCCESSFULLY

Data in the list
Data = 10
Data = 20
Data = 30
Data = 40
Data = 50

Enter the node position you want to delete: 4
SUCCESSFULLY DELETED NODE FROM MIDDLE OF LIST

Data in the list
Data = 10
Data = 20
Data = 30
Data = 50

Happy coding ;)


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