Reverse Linked List

1. next = current->next;   // aage ka save karein
2. current->next = prev;   // link peeche palten
3. prev = current;         // prev aage badhayein
4. current = next;         // current aage badhayein

#include <stdio.h>
#include <stdlib.h>
struct Node { int data; struct Node *next; };

struct Node* reverse(struct Node *head) {
    struct Node *prev = NULL, *current = head, *next = NULL;
    while (current != NULL) {
        next = current->next;    // 1. aage save
        current->next = prev;    // 2. flip
        prev = current;          // 3. prev aage
        current = next;          // 4. current aage
    }
    return prev;                 // naya head
}
void printList(struct Node *n) {
    while (n) { printf("%d -> ", n->data); n = n->next; }
    printf("NULL\n");
}
struct Node* newNode(int v) {
    struct Node *n = malloc(sizeof(struct Node));
    n->data = v; n->next = NULL; return n;
}
int main() {
    struct Node *head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);

    printf("Original: "); printList(head);
    head = reverse(head);
    printf("Reversed: "); printList(head);
    return 0;
}