[Leet Code] Middle of the Linked List

Matthew Boyd
1 min readJan 24, 2021

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

Problem:

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.

Solution:

# Definition for singly-linked list.
# class ListNode(object):
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution(object):
def middleNode(self, head):
"""
:type head: ListNode
:rtype: ListNode
"""
elements = []
self.traverse(head, elements )
return elements[(len(elements) / 2)]

def traverse(self, head, elements):
if head.next:
elements.append(head)
self.traverse(head.next,elements)
else:
elements.append(head)
return

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Matthew Boyd
Matthew Boyd

Written by Matthew Boyd

Learning, and posting my findings!

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