Palindrome Linked List

Step0 / 10

PhaseInitialize

Nodes5

Result—

Code

1def isPalindrome(head):
2    if not head or not head.next:
3        return True
4 
5    # Find middle using slow/fast pointers
6    slow = fast = head
7    while fast and fast.next:
8        slow = slow.next
9        fast = fast.next.next
10 
11    # Reverse second half
12    prev = None
13    curr = slow
14    while curr:
15        next_node = curr.next
16        curr.next = prev
17        prev = curr
18        curr = next_node
19 
20    # Compare both halves
21    left = head
22    right = prev
23    while right:
24        if left.val != right.val:
25            return False
26        left = left.next
27        right = right.next
28 
29    return True

Function definition

Linked List

INIT

Step

0 / 10

Phase

Initialize

Nodes

Progress

Processing

Checking if the linked list is a palindrome...

Pointer State

Pointers

slow

fast

left

null

right

null

Key Insight

Find the middle with slow/fast pointers, reverse the second half, then compare from both ends. No extra space needed.

Explanation

Setup

Initialize Pointers

Set both slow and fast pointers to the head of the list.

💡 Tip

Slow moves 1 step, fast moves 2 steps per iteration.