Palindrome Linked List

Palindrome Linked List

问题：

Given a singly linked list, determine if it is a palindrome.

Follow up:
Could you do it in O(n) time and O(1) space?

思路：

　　先选择中间的节点+反转链表

我的代码：

public class Solution {

    public boolean isPalindrome(ListNode head) {

        if(head == null)    return true;

        

        ListNode mid = getMiddle(head);

        ListNode reverse = getReverse(mid);

        

        while(head!=null && reverse!=null)

        {

            if(head.val == reverse.val)

            {

                head = head.next;

                reverse = reverse.next; 

            }

            else return false;

        }

        

        return true;

        

    }

    public ListNode getMiddle(ListNode head)

    {

        ListNode slow = head;

        ListNode fast = head.next;

        while(fast!=null && fast.next!=null)

        {

            fast = fast.next.next;

            slow = slow.next;

        }

        return slow;

    }

    public ListNode getReverse(ListNode head)

    {

        ListNode dummy = new ListNode(-1);

        while(head != null)

        {

            ListNode next = head.next;

            head.next = dummy.next;

            dummy.next = head;

            head = next;

        }

        return dummy.next;

    }

}

View Code

 

反思：

• 反转链表好久没写了，竟然都忘记了，代码果然好久没写就是不行啊，幸好在同学的指导下面又重新学会了。
• palindrome的方法就是反转，从头开始反转，从中间反转，让反转后的等于前面的反转。