LinkedList Palindrome - Stack

LinkedListPalindromeStack.py

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

class Solution:
    def isPalindrome(self, head: ListNode) -> bool:
        
        # low hanging fruit
        if not head:
            return True
        
        palindrome = True
        stack = []
        tmpNode = ListNode() # tmpNode is going to be used to load the stack
        tmpNode = head
        
        # 1.) Traverse the list from head to tail and push every visited node to the stack
        while tmpNode is not None: # None is Python's equivalent to null
            stack.append(tmpNode.val)
            tmpNode = tmpNode.next
        '''    
        2.) Traverse the list again. For every visited node, pop a node from the stack and coompare the val of the popped node with the current node in the LL
        If the current val of the node in the LL does not equal the val of node popped from the stack, return False. We clearly don't have a palindrome
        If the val of the node in the LL equals the val of thge node popped from the stack, continue. We will finish when we reach the end of the LL or find a mismatch
        '''
        while head is not None:
            stackVal = stack.pop()
            if head.val != stackVal:
                palindrome = False
                break
            else:
                palindrome = True
                
            head = head.next
            
        return palindrome

LeetCode 234. Palindrome Linked List
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