LeetCode 234. 回文链表 java

示例 1:

输入: 1->2
输出: false

示例 2:

输入: 1->2->2->1
输出: true

JAVA 代码：

class Solution {
    public boolean isPalindrome(ListNode head) {
	    ListNode fast = head;
		ListNode slow = head;
		ListNode prev = null;
		while (fast != null && slow != null) {
			fast = fast.next == null ? fast.next : fast.next.next;
			slow = slow.next;
		}
		// reverse
		while (slow != null) {
			ListNode ovn = slow.next;
			slow.next = prev;
			prev = slow;
			slow = ovn;
		}
		// check
		while (head != null && prev != null) {
			if (head.val != prev.val) {
				return false;
			}
			head = head.next;
			prev = prev.next;
		}
		return true;
    }
}