Leetcode 题目解析之 Palindrome Linked List

    public boolean isPalindrome(ListNode head) {

        if (head == null || head.next == null) {
            return true;
        }

        ListNode slow = head;
        ListNode fast = head;

        // 找到链表中点
        while (fast != null && fast.next != null) {
            slow = slow.next;
            fast = fast.next.next;
        }

        // 翻转后段链表
        ListNode tail = reverseList(slow);

        while (head != slow) {
            if (head.val != tail.val) {
                return false;
            }
            head = head.next;
            tail = tail.next;
        }

        return true;
    }

    public ListNode reverseList(ListNode head) {

        if (head == null) {
            return null;
        }

        if (head.next == null) {
            return head;
        }

        ListNode tail = head.next;
        ListNode reversed = reverseList(head.next);

        // 前后翻转tail和head
        tail.next = head;
        head.next = null;

        return reversed;

    }