回文链表leecode

偶数情况

public boolean isPalindrome(ListNode head) {
        if (head == null) {
            return true;
        }

        ListNode fast = head;
        ListNode slow = head;

        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            slow = slow.next;
        }

        //反转
        ListNode cur = slow.next;
        while (cur != null) {
            ListNode curNext = cur.next;
            cur.next = slow;
            slow = cur;
            cur = curNext;
        }

        while (head != slow) {
            //走之前先判断
            if (head.val != slow.val) {
                return false;
            }

            //偶数情况
            if (head.next == slow) {
                return true;
            }
            head = head.next;
            slow = slow.next;
        }
        return true;
    }

奇数情况

public boolean isPalindrome(ListNode head) {
        if (head == null) {
            return true;
        }

        ListNode fast = head;
        ListNode slow = head;

        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            slow = slow.next;
        }

        //反转
        ListNode cur = slow.next;
        while (cur != null) {
            ListNode curNext = cur.next;
            cur.next = slow;
            slow = cur;
            cur = curNext;
        }

        while (head != slow) {
            //走之前先判断
            if (head.val != slow.val) {
                return false;
            }

            //偶数情况
            if (head.next == slow) {
                return true;
            }
            head = head.next;
            slow = slow.next;
        }
        return true;
    }