'''
876. Middle of the Linked List

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.
'''

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next

from typing import List


class ListNode:

    def __init__(self, x, next=None):
        self.val = x
        self.next = next


class LinkedList:

    def __init__(self, vals: List[int] = []):
        cur_node = None
        self.head = None
        self.d = dict()

        for i in range(len(vals)):
            
            node = None

            if vals[i] in self.d:
                node = self.d[vals[i]]
            else:
                node = ListNode(vals[i])
                self.d[vals[i]] = node
            
            if cur_node:
                cur_node.next = node
            
            cur_node = node

            if not self.head:
                self.head = cur_node


class Solution:

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


sol = Solution()

ll: LinkedList = LinkedList([1,2,3,4,5])
head: ListNode = ll.head
res: ListNode = sol.middleNode(head)
print(res.val)

ll: LinkedList = LinkedList([1,2,3,4,5,6])
head: ListNode = ll.head
res: ListNode = sol.middleNode(head)
print(res.val)
        
        
        