Odd-length palindrome
Input
[1, 2, 3, 2, 1]
Output
True
The sequence reads the same forwards and backwards.
Full lesson preview
Check if a linked list is a palindrome
Determine whether a singly linked list reads the same forwards and backwards.
Python practice18 minLinked ListsIntermediateLast updated March 27, 2026
Problem statement
Given a singly linked list (input provided as a Python list of values), determine whether it is a palindrome. You should construct the linked list, then check palindrome by finding the midpoint, reversing the second half in-place, and comparing nodes. Restore the list if you wish (not required). Return True if the list is a palindrome, False otherwise.
Edge cases: empty list and single-node list are palindromes.
Task
Given a list as a Python list, build a linked list, and check if it is a palindrome in O(n) time and O(1) extra linked-list pointer space (excluding input/output lists).
Examples
Input format
A single Python list representing node values of the linked list.
Output format
Boolean True/False indicating palindrome status.
Constraints
- Aim for O(n) time and O(1) additional linked-list pointers. Values are integers. List size can be zero.
Samples
Sample 1
Input
[1, 2, 2, 1]
Output
True
Even-length palindrome.