0876-Middle-of-the-Linked-List.py

'''
Given a non-empty, singly linked list with head node head, return a middle node of linked list.

If there are two middle nodes, return the second middle node.

 

Example 1:

Input: [1,2,3,4,5]
Output: Node 3 from this list (Serialization: [3,4,5])
The returned node has value 3.  (The judge's serialization of this node is [3,4,5]).
Note that we returned a ListNode object ans, such that:
ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.
Example 2:

Input: [1,2,3,4,5,6]
Output: Node 4 from this list (Serialization: [4,5,6])
Since the list has two middle nodes with values 3 and 4, we return the second one.
 

Note:

The number of nodes in the given list will be between 1 and 100.
'''
# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

#Time Complexity - O(n), Space Complexity - O(1)
class Solution:
    def middleNode(self, head: ListNode) -> ListNode:  
        mid = end = head
        while end and end.next:
            mid = mid.next
            end = end.next.next
        return mid