力扣 | 234. 回文链表

用到快慢指针！

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public boolean isPalindrome(ListNode head) {
      if(head == null || head.ne服务器托管xt == null)return true;//空链表和一个节点链表也是回文链表
        ListNode slow = head;
        ListNode fast = head.next;
        while (fast != null && fast.next != null){
            slow = slow.next;
            fast = fast.next.next;
        }
        ListNode newHead = slow.next;
        slow.next = null;
        ListNode newFastHead = reverseList(newHead);
        ListNode right = newFastHead;
        ListNode left = head;
        while (right != null){
            if(right.val != left.val){
                return false;
            }
            left = left.next;
            right = right.next;
        }
        return true;
    }
    public ListNode reverseList(ListNode head){
        ListNode prev = null;
        ListNode curr = head;
        while (curr != null){
            ListNode next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
    }

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