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Reverse a linked list without changing links between nodes (Data reverse only)
Here, in this page we will discuss Reverse a linked list without changing links between nodes in C. We create a vector and store the elements of the linked list and them change the linked list node data by iterating the vector in reverse manner.


Algorithm :
- Create a node say current and set it to head.
- Now, Create a variable to store size of linked list. We will iterate over all nodes of linked list and increment the size variable by 1 and set current to next node. Repeat this till the current node does not become NULL.
- Create an array of size (size) to store the node value in it.And create a variable say x points to last index of the array. We will iterate over all nodes of linked list and insert the current node data in that array position and decrement the x by 1 and set current to next node. Repeat this till the current node does not become NULL.
- Now, again set current to head and take a variable say x and set it to 0.
- Now, change the current node data with array[x] and increment the x by 1 and set current to next node. Repeat this till current node does not become NULL.
- In this way we can Reverse a linked list without changing links between nodes in C.


Code in C based on above Algorithm
Run
#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* current = *head_ref; int size =0; while (current != NULL) { size++; current = current->next; } int a[size]; int x=size-1; current = *head_ref; while (current != NULL) { a[x--] = current->data; current = current->next; } current = *head_ref; x=0; while (current != NULL) { current->data = a[x++]; current = current->next; } } /* 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 code*/ 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; struct Node* node3 = NULL; struct Node* node4 = NULL; // allocate 3 nodes in the heap head = (struct Node*)malloc(sizeof(struct Node)); node2 = (struct Node*)malloc(sizeof(struct Node)); node3 = (struct Node*)malloc(sizeof(struct Node)); node4 = (struct Node*)malloc(sizeof(struct Node)); head->data = 5; // data set for head node head->next = node2; // next pointer assigned to address of node2 node2->data = 10; node2->next = node3; node3->data = 15; node3->next = node4; node4->data = 20; node4->next = NULL; printf("Given Linked list: "); printList(head); reverse(&head); printf("\n\nReversed Linked list: "); printList(head); return 0; }
Output:
Given Linked list: 5 10 15 20
Reversed Linked list: 20 15 10 5
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