C Program for Reversing a linked list by changing links between the nodes
Reverse a Linked List by changing the links between the nodes
Here we will learn how to code a C program for reversing a linked list by changing the links between the nodes. That is, in this program we will be reversing the pointers of the node. i.e, if the user entered 1,2,3,4,5 in the linked list, the linked list will be reversed and the output will be 5,4,3,2,1. Let’s see how to code a C program for this problem
How to reverse a Linked List by changing the links between the nodes
- Step 1 – We will take three pointers ptr1, ptr2 and ptr3. Initially the first and the third pointer will point NULL, and the second pointer will point the head.
- Step 2 – We will iterate through the linked list, swapping the value of these 3 pointers.
- Step 3 – ptr3 will now point the second node of the linked, and ptr2 will be removed from the linked list.
- Step 4 – Now ptr1 will point the removed node.
- Step 5 – ptr2 node will point ptr1 node.
- Step 6 – All the three pointers will be moved by +1.
- Step 7 – The above steps will be repeated until ptr3 points the NULL.
- Step 8 – Than in the last step, the last node will become the HEAD of the linked list
Algorithm for reversing the data of a linked list
- START WHILE
- NEXT=CURRENT->NEXTPTR
- CURRENT->NEXTPTR=PREV
- PREV=CURRENT
- CURRENT=NEXT
- END WHEN CURRENT=NULL
- HEAD_ADDR=PREV
C Program for Reversing a Linked List, by changing links between the nodes
Run
#include<stdio.h>
#include<stdlib.h>
/* Link list node */
struct Node
{
int data;
struct Node *next;
};
/* Function to reverse the linked list */
void reverseLinkedList (struct Node **head_addr)
{
struct Node *prev = NULL;
struct Node *current = *head_addr;
struct Node *next = NULL;
while (current != NULL)
{
// Store next
next = current->next;
// Reverse current node's pointer
current->next = prev;
// Move pointers one position ahead.
prev = current;
current = next;
}
*head_addr = prev;
}
/* Function to push a node */
void insert (struct Node **head_addr, int new_data)
{
struct Node *new_node = (struct Node *) malloc (sizeof (struct Node));
new_node->data = new_data;
new_node->next = (*head_addr);
(*head_addr) = new_node;
}
/* Function to print linked list */
void display (struct Node *head)
{
struct Node *temp = head;
while (temp != NULL)
{
printf ("%d ", temp->data);
temp = temp->next;
}
}
int main ()
{
int i, n, data;
/* Start with the empty list */
struct Node *head = NULL;
printf ("Enter the number of nodes: ");
scanf ("%d", &n);
printf ("\nEnter the data in the nodes: ");
for (i = 0; i < n; i++)
{
scanf ("%d", &data);
insert (&head, data);
}
printf ("\nGiven linked list: ");
reverseLinkedList (&head);
display (head);
printf ("\n\nReversed Linked list: ");
reverseLinkedList (&head);
display (head);
return 0;
}
Output
Enter the number of nodes: 5
Enter the data in the nodes: 1 2 3 4 5
Given linked list: 1 2 3 4 5
Reversed Linked list: 5 4 3 2 1
Fun Fact
Problems for performing different operations on Linked List are asked in various coding competitions, either directly or in the form of a logical problem. Here we have described one of the manner of reversing a Linked list, but there are few more ways of reversing a linked list according to your needs, like Reversing it without changing the links, or just reverse printing the data.
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