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;
    }
}

 

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。