Stanley Zhao

Software Engineer

Interview Prep Day 4

Dec 06, 2022
1 min read

Day 4

LeetCode 206. Reverse Linked List

Two Pointer Solution --> O(n) time (while loop)

// @param {ListNode} head // @return {ListNode} var reverseList = function (head) { let [prev, curr, next] = [null, head, null]; while (curr != null) { next =; = prev; prev = curr; curr = next; } return prev; };
  • I'll use [1,2,3,4,5] as an example for our linked list.
  • head provides us the reference to the very beginning element of our linked list
    • Declare prev as null, curr as head, and next as null.
    • We will keep executing until we reach the end of the linked list (when we end up at null)
  • We set next equal to, which would be 2.
  • Set equal to prev, which starts as null.
  • Now set prev equal to curr, which is currently 1.
  • Set curr equal to next, which is 2.
  • What ends up happening is our current element is now 2 and it's .next is pointing towards 1.

This problem was conceptually challenging. The idea of list elements changing order while holding references was confusing 😅. Definitely need to study these.