// Node class for singly linked list
class ListNode {
value: number; // data stored in the node
next: ListNode | null; // reference to the next node
constructor(value: number) {
this.value = value;
this.next = null;
}
}
// Reverse the linked list in-place
function reverseList(head: ListNode | null): ListNode | null {
let prev: ListNode | null = null; // will become the new head
let current: ListNode | null = head; // pointer to traverse the list
while (current !== null) {
const nextNode: ListNode | null = current.next; // save next node
current.next = prev; // reverse the link
prev = current; // move prev forward
current = nextNode; // move current forward
}
return prev; // prev is the new head
}
// Print the linked list
function printList(head: ListNode | null): void {
let temp: ListNode | null = head;
let output: string = "";
while (temp !== null) {
output += temp.value;
if (temp.next !== null) output += " -> ";
temp = temp.next;
}
console.log(output);
}
// Build a sample list: 1 -> 2 -> 3 -> 4 -> 5
let head: ListNode = new ListNode(1);
head.next = new ListNode(2);
head.next.next = new ListNode(3);
head.next.next.next = new ListNode(4);
head.next.next.next.next = new ListNode(5);
console.log("Original list:");
printList(head);
// Reverse the list
head = reverseList(head)!;
console.log("Reversed list:");
printList(head);
/*
run:
Original list:
1 -> 2 -> 3 -> 4 -> 5
Reversed list:
5 -> 4 -> 3 -> 2 -> 1
*/
