Iterative Method
- Initialize three pointers prev as NULL, curr as head and next as NULL.
- Iterate trough the linked list. In loop, do following.
// Before changing next of current,
// store next node
next = curr->next
// Now change next of current
// This is where actual reversing happens
curr->next = prev
// Move prev and curr one step forward
prev = curr
curr = next
// Iterative C program to reverse a linked list
#include <stdio.h>
#include <stdlib.h>
/* Link list node */
struct Node {
int data;
struct Node* next;
};
/* Function to reverse the linked list */
static void reverse(struct Node** head_ref)
{
struct Node* prev = NULL;
struct Node* current = *head_ref;
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_ref = prev;
}
/* Function to push a node */
void push(struct Node** head_ref, int new_data)
{
struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
new_node->data = new_data;
new_node->next = (*head_ref);
(*head_ref) = new_node;
}
/* Function to print linked list */
void printList(struct Node* head)
{
struct Node* temp = head;
while (temp != NULL) {
printf("%d ", temp->data);
temp = temp->next;
}
}
/* Driver program to test above function*/
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
push(&head, 20);
push(&head, 4);
push(&head, 15);
push(&head, 85);
printf("Given linked list\n");
printList(head);
reverse(&head);
printf("\nReversed Linked list \n");
printList(head);
getchar();
}
Time Complexity: O(n)
Space Complexity: O(1)
Ref: https://www.geeksforgeeks.org/reverse-a-linked-list/
