Middle of the Linked List

Problem

Given the head of a singly linked list, return the middle node of the linked list. If there are two middle nodes, return the second middle node.

Examples

The brute-force approach

Count the total number of nodes in one pass, then traverse to the middle in a second pass.

count = 0
curr = head
while curr:
    count += 1
    curr = curr.next

curr = head
for _ in range(count // 2):
    curr = curr.next

return curr

Two separate passes over the list. Not wrong, but a fast and slow pointer can find the middle in a single pass without needing to count first.

Spotting the pattern

This is a Linked List problem. The key question to ask yourself:

Without knowing the length of the list, how do I find the middle in one pass?

Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.