Reverse a Linked List - Netflix Interview Question & Solution

Reverse a Linked List

Netflix

Linked List

Two Pointers

Given the head of a singly linked list, reverse the list, and return the reversed list's head.

Example:

Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]

Solution Walkthrough

The iterative approach reverses the list in place by walking through it once and flipping each node's next pointer to point backward instead of forward.

Keep three pointers: prev (initially null), curr (initially head), and a temporary next.
While curr is not null:
- Save curr.next into next before you overwrite it.
- Point curr.next back to prev.
- Move prev up to curr, and curr up to next.
When the loop ends, curr is null and prev is sitting on the new head — return it.

This runs in O(n) time with O(1) extra space, since every node is visited exactly once and no new list is allocated.

function reverseList(head) {
    let prev = null;
    let curr = head;

    while (curr !== null) {
        const next = curr.next; // save the rest of the list
        curr.next = prev;       // reverse the pointer
        prev = curr;            // advance prev
        curr = next;            // advance curr
    }

    return prev; // prev is now the new head
}

Related Algorithms

Singly Linked List →