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

isPalindrome.py

class Solution:
    def isPalindrome(self, head: Optional[ListNode]) -> bool:
        """ 
        1 2 3 4 5
        1 2
        2 4
        3 None
        """
        slow, fast =  head, head.next
        
        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
            
        print(slow.val)
        
        """
        Head->1->2->3->4->5->None
        p = 5
        c = N
        n = N
        5->4->3->None
        """
        prev_node = None
        curr_node = slow
        
        while curr_node:
            next_node = curr_node.next
            curr_node.next = prev_node
            prev_node, curr_node = curr_node, next_node
            
        left = head
        right = prev_node
        
        while left and right:
            if left.val != right.val:
                return False
            left = left.next
            right = right.next
        return True
        
        
        

isPalindrome2.py

class Solution:
    def isPalindrome(self, head: Optional[ListNode]) -> bool:
        stack = []
        node = head
        
        while node:
            stack.append(node.val)
            node = node.next
        
        left = 0
        right = len(stack) - 1
        
        while left < right:
            if stack[left] != stack[right]:
                return False
            left += 1
            right -= 1
            
        return True