Middle of the linked list

We will take two pointers, one will move one step at a time and the other will move two steps at a time. When the second pointer reaches the end of the list, the first pointer will be at the middle of the list.

class Solution:
    def middleNode(self, head: ListNode) -> ListNode:
        slow = fast = head
        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
        return slow

Time complexity: O(n)
Space complexity: O(1)