Given a singly linked list, determine if it is a palindrome.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
| public class Solution {
public boolean isPalindrome(ListNode head) {
if (head == null || head.next == null) {
return true;
}
ListNode fast = head.next;
ListNode slow = head;
while (fast != null && fast.next != null) {
fast = fast.next.next;
slow = slow.next;
}
ListNode half = reverse(slow.next);
fast = head;
while (half != null && fast != null) {
if (half.val != fast.val) {
return false;
}
half = half.next;
fast = fast.next;
}
return true;
}
private ListNode reverse(ListNode head) {
if (head == null || head.next == null) {
return head;
}
ListNode cursor = head;
ListNode next = cursor.next;
ListNode tmp;
cursor.next = null;
while (next != null) {
tmp = next.next;
next.next = cursor;
cursor = next;
if (tmp != null) {
next = tmp;
} else {
break;
}
}
return next;
}
}
|