Palindromic Linked List

L6 Medium Linked List

Concept

Because linked lists are only forward-accessible, checking symmetry usually means copying values into an array and using two indices.

Given the head of a singly linked list, return true if the values form a palindrome (read the same forwards and backwards).

Examples

▸ head = [1, 2, 2, 1]

→ true

▸ head = [1, 2]

→ false

▸ head = [1]

→ true

Progressive Hints

Hint 1 · Nudge

If you could read the list backwards it'd be trivial, so just copy it into something that supports both ends.

Hint 2 · Plan

Copy every value into an array, then compare from both ends inward, exactly like the word palindrome. Any mismatch means false.

Hint 3 · Approach

values = [], cur = head. While cur: append cur.val; cur = cur.next. Compare from both ends inward and return false on any mismatch.

Output

// Run your code to see the output here.