[LeetCode] 234. Palindrome Linked List

Problem : https://leetcode.com/problems/palindrome-linked-list/

Use post-order traversal to check the input string recursively.

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def isPalindrome(self, head: ListNode) -> bool:
        left = 0
        
        def postorder(node, right):
            nonlocal head
            nonlocal left
            
            if node:
                tmp = postorder(node.next, right + 1)
                if not tmp:
                    return tmp
                
                if left < right:
                    if node.val != head.val:
                        return False
                
                    head = head.next
                    left += 1
                
                return True
                
            return True
        
        return postorder(head, 0)