Another warm-up question from the archives.

The editorial solution, fast-and-slow-pointer, is very cute. I’m not sure how it’s preferable over separating the length (“fast”) calculation from the actual-find-calculation (“slow”). We’re doing the same traversals, but presumably with better locality?

class Solution:
    def middleNode(self, head: Optional[ListNode]) -> Optional[ListNode]:
        l = 0
        n = head
        while n is not None:
            n = n.next
            l += 1

        n = head
        for i in range(l//2):
            n = n.next
        
        return n