876. Middle of the Linked List

https://leetcode.com/problems/middle-of-the-linked-list/

JavaScript

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var middleNode = function(head) {
  let fast = head
  let slow = head

  while (fast && fast.next) {
    fast = fast.next.next
    slow = slow.next
  }

  return slow
}

Python

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None


class Solution:

    def middleNode(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        fast = slow = head
        while fast and fast.next:
            fast = fast.next.next
            slow = slow.next
        return slow