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Solution.java
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Solution.java
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package g0201_0300.s0234_palindrome_linked_list;
// #Easy #Top_100_Liked_Questions #Two_Pointers #Stack #Linked_List #Recursion
// #Level_2_Day_3_Linked_List #Udemy_Linked_List #Big_O_Time_O(n)_Space_O(1)
// #2022_07_04_Time_6_ms_(76.07%)_Space_97.6_MB_(56.14%)
import com_github_leetcode.ListNode;
/*
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
public class Solution {
public boolean isPalindrome(ListNode head) {
int len = 0;
ListNode right = head;
// Culculate the length
while (right != null) {
right = right.next;
len++;
}
// Reverse the right half of the list
len = len / 2;
right = head;
for (int i = 0; i < len; i++) {
right = right.next;
}
ListNode prev = null;
while (right != null) {
ListNode next = right.next;
right.next = prev;
prev = right;
right = next;
}
// Compare left half and right half
for (int i = 0; i < len; i++) {
if (prev != null && head.val == prev.val) {
head = head.next;
prev = prev.next;
} else {
return false;
}
}
return true;
}
}