Middle of the Linked List - Leetcode 876 - Python 

i did a similar question. it was leetcode 2095, "delete the middle node of a linked list" from leetcode 75. initially, i counted the nodes and from there, i found out where the middle node was by taking the count / 2 and then went through the linked list again to delete the middle node. i then tried the slow and fast pointer approach, but to my surprise, it resulted in near identical runtimes (2 ms difference) and memory usage. i assumed the slow and fast pointer approach would be faster since we only pass through the linked list once. edit: i realized after rewatching the video that we technically pass through the linked list twice. so, it makes sense why it resulted in identical results.

awesome thank you so much for all of your clean and simple code solution explanation.

I was always wondering why they use fast and fast.next, I traced it saw the solution and was still confused, thankyou for this.

Thanks! In case any of you are wondering what to do if the definition of Middle Element changes for a linked list with even number of elements, i.e. if in the linked list with values [1,2,3,4,5,6], the middle element is 3 and not 4 as given in the problem, here's the solution with two pointer method: public class Solution { public ListNode MiddleNode(ListNode head) { ListNode fast = head; ListNode slow = head; while(fast.next!=null && fast.next.next!=null){ slow = slow.next; fast = fast.next.next; } return slow; } }

definetly a neet code!!

Thanks for the video explanation, and I understand conceptually why it works and how to implement it in code (typescript in my case). Where I'm lost is the given input and output values. Can you please explain why in the question it gives the input and output as an array of numbers even though the class is ListNode, which is clearly defined as not simply an array of numbers? I really don't understand.

It's funny working through Grind 75, I think we used a similar approach to account for cycles in a linkedlist and where to break out of it, I think it was 141

Thanks. Keep uploading videos!

Hi Neetcode, Thank you for a great solution. is it your next channel?

Hi Neetcode, can we get weekly contest solution video.

I solved it similarly in java and I got a NullPointerExpection because fast.next.next is not defined. What if the fast.next is the last node? So I solved by splitting that line into two parts, this is the whole logic I wrote: while(fast != null && fast.next != null){ fast = fast.next; if(fast == null) break; if(fast.next != null) fast = fast.next; slow = slow.next; }

God

eu acho que seria O(N/2)

Can you explain also worst and best case scenario , and big O notation

i cant understand why we wrote while fast and fast.next: What does it mean? While fast and fast.next != what? !=0 or !=True? how we can rewrite it to understand better

Stop. It's not a real neetcode. What the f?