234. Palindrome Linked List

#java #algorithms #leetcode #100daysofcode

Problem Statement:

Given the head of a singly linked list, return true if it is a
palindrome or false otherwise.

Example 1:

Input: head = [1,2,2,1]
Output: true

Example 2:

Input: head = [1,2]
Output: false

Constraints:

The number of nodes in the list is in the range [1, 105].
0 <= Node.val <= 9

Solution:

Code:

public class Solution {
    public boolean isPalindrome(ListNode head) {
        ListNode slow = head, fast = head, prev, temp;
        while (fast != null && fast.next != null) {
            slow = slow.next;
            fast = fast.next.next;
        }
        prev = slow;
        slow = slow.next;
        prev.next = null;
        while (slow != null) {
            temp = slow.next;
            slow.next = prev;
            prev = slow;
            slow = temp;
        }
        fast = head;
        slow = prev;
        while (slow != null) {
            if (fast.val != slow.val)
                return false;
            fast = fast.next;
            slow = slow.next;
        }
        return true;
    }

}