[LeetCode]234. Palindrome Linked List

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

思路：快慢指针，慢指针一次跳一个，快指针一次跳两个，这样快指针跳完慢指针就是中心点

这样还是要用到n/2的栈空间，使用反转链表法可以实现1空间

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public boolean isPalindrome(ListNode head) {        ListNode slow,fast;        slow=head;        fast=head;        Stack<ListNode> stack=new Stack<ListNode>();        while(fast!=null){            stack.push(slow);            slow=slow.next;            fast=fast.next;            if(fast==null){                stack.pop();                break;            }            fast=fast.next;        }        while(slow!=null){            if(slow.val!=stack.pop().val){                return false;            }            slow=slow.next;        }        return true;    }}