C Program to Insert a Node at the middle of a Linked List

August 5, 2023

Insertion in the middle of a Linked List in C

We will look at different methods to do insertion in the middle of a Singly Linked list in C

We will look at two different methods –

Method 1: Uses additional size variable to keep track of Linked List Size
Method 2: No additional variable, we calculate the size in realtime

Now lets have look on how to write a routine to add a node in the middle of the linked list

Reverse a linked list without changing links between nodes

Reverse a linked list by changing links between nodes

Print reverse of a linked list without actually reversing

Search an element in a linked list

Insertion in a Sorted Linked List

Method 1

Method 2

Method 1

Run

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

struct Node
{
  int data;
  struct Node *next;
};

int size = 0;

void insertMiddle (struct Node **head, int data)
{

  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if the LL was empty
  if (*head == NULL)
    {
      newNode->data = data;
      newNode->next = *head;
      *head = newNode;
      size++;
      return;
    }

  // otherwise
  struct Node *temp = *head;

  // find correct insertion position for middle
  int mid = (size % 2 == 0) ? (size / 2) : (size + 1) / 2;

  // traverse to current mid position
  while (--mid)
    {
      temp = temp->next;
    }

  newNode->next = temp->next;
  temp->next = newNode;
  size++;

}

void display (struct Node *node)
{
  printf ("Linked List : ");

  // as linked list will end when Node is Null
  while (node != NULL)
    {
      printf ("%d ", node->data);
      node = node->next;
    }
  printf ("\n\n");
}

int main ()
{
  //creating 2 pointers of type struct Node
  //So these can point to address of struct type variable
  struct Node *head = NULL;
  struct Node *node2 = NULL;

  // allocate 3 nodes in the heap 
  head = (struct Node *) malloc (sizeof (struct Node));
  node2 = (struct Node *) malloc (sizeof (struct Node));

  head->data = 10;		// data set for head node 
  head->next = node2;		// next pointer assigned to address of node2 

  node2->data = 50;
  node2->next = NULL;

  size = 2;

  display (head);

  insertMiddle (&head, 20);
  display (head);

  insertMiddle (&head, 40);
  display (head);

  insertMiddle (&head, 30);
  display (head);

  return 0;
}

Output

Linked List : 
10 50 

Linked List : 
10 20 50 

Linked List : 
10 20 40 50 

Linked List : 
10 20 30 40 50

Method 2

Run

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

struct Node
{
  int data;
  struct Node *next;
};

int getCurrSize (struct Node *node)
{
  int size = 0;

  while (node != NULL)
    {
      node = node->next;
      size++;
    }
  return size;
}

void insertMiddle (struct Node **head, int data)
{

  struct Node *newNode = (struct Node *) malloc (sizeof (struct Node));
  newNode->data = data;

  // if the LL was empty
  if (*head == NULL)
    {
      newNode->data = data;
      newNode->next = *head;
      *head = newNode;
      return;
    }

  // otherwise
  struct Node *temp = *head;

  int size = getCurrSize (*head);

  // find correct insertion position for middle
  int mid = (size % 2 == 0) ? (size / 2) : (size + 1) / 2;

  // traverse to current mid position
  while (--mid)
    {
      temp = temp->next;
    }

  newNode->next = temp->next;
  temp->next = newNode;

}

void display (struct Node *node)
{
  printf ("Linked List : ");

  // as linked list will end when Node is Null
  while (node != NULL)
    {
      printf ("%d ", node->data);
      node = node->next;
    }
  printf ("\n\n");
}

int main ()
{
  //creating 4 pointers of type struct Node
  //So these can point to address of struct type variable
  struct Node *head = NULL;
  struct Node *node2 = NULL;

  // allocate 3 nodes in the heap 
  head = (struct Node *) malloc (sizeof (struct Node));
  node2 = (struct Node *) malloc (sizeof (struct Node));

  head->data = 10;		// data set for head node 
  head->next = node2;		// next pointer assigned to address of node2 

  node2->data = 50;
  node2->next = NULL;

  display (head);

  insertMiddle (&head, 20);
  display (head);

  insertMiddle (&head, 40);
  display (head);

  insertMiddle (&head, 30);
  display (head);

  return 0;
}

Output

Linked List : 
10 50 

Linked List : 
10 20 50 

Linked List : 
10 20 40 50 

Linked List : 
10 20 30 40 50

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Singly Linked List

Introduction to Linked List in Data Structure
Click Here
Linked List in –
C | C++ | Java
Singly Linked List in –
C | C++ | Java
Insertion in singly Linked List –
C | C++ | Java
Insertion at beginning in singly Linked List –
C | C++ | Java
Insertion at n^th position in singly Linked List –
C | C++ | Java
Insertion at end in singly Linked List –
C | C++ | Java
Deletion in singly Linked List –
C | C++ | Java
Deletion from beginning in singly linked list :
C | C++ | Java
Deletion from n^th position in singly linked list :
C | C++ | Java
Deletion from end in singly linked list :
C | C++ | Java
Linked List Insertion and Deletion –
C | C++ | Java
Reverse a linked list without changing links between nodes (Data reverse only) –
C | C++ | Java
Reverse a linked list by changing links between nodes –
C | C++ | Java
Print reverse of a linked list without actually reversing –
C |C++ | Java
Print reverse of a linked list without actually reversing –
C |C++ | Java
Insertion in the middle Singly Linked List –
C | C++ | Java
Insertion in a Sorted Linked List –
C | C++ | Java
Delete alternate nodes of a Linked List –
C | C++ | Java
Find middle of the linked list –
C | C++ | Java
Reverse a linked list in groups of given size –
C | C++ | Java
Find kth node from end of the linked list –
C | C++ | Java
Append the last n nodes of a linked list to the beginning of the list –
C | C++ | Java
Check whether linked list is palindrome or not –
C | C++ | Java
Fold a Linked List –
C | C++ | Java
Insert at given Position –
C | C++ | Java
Deletion at given Position –
C | C++ | Java