Linked List/Palindrome Linked ListEasy

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Palindrome Linked List

Linked List·Easy

Given the head of a singly linked list, return true if it reads the same forward and backward.

Input/output convention for this exercise: the list is passed as an array of values; the helpers in the starter (ListNode, arrayToList, listToArray) let you convert to a real linked list and back.

The textbook O(n)-time, O(1)-space solution finds the middle with slow/fast pointers, reverses the second half in place, then walks both halves comparing values. An O(n)-space copy-to-array approach is also acceptable.

Examples

Input: values = [1,2,2,1]

Output: true

Input: values = [1,2]

Output: false

Input: values = [1,2,3,2,1]

Output: true

Constraints

0 <= values.length <= 10^5
0 <= values[i] <= 9

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Tests

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Passed32 ms

First attempt — retry to track metric movement here.

Your approach

Pattern:Linked List
Time:O(N)
Space:O(1)

Complete approach — pattern and complexity both named.

Coach

What you got right

You correctly matched the sorted input requirement and implemented a linear-time scan using two pointers.

Where it diverged

No divergence detected. The code correctly aligns with the stated approach.

Next attempt: focus on

Try solving related sliding window problems to build familiarity with two-pointer variants.

Signals

No signals fired — clean run, you stayed in flow.