234. Palindrome Linked List

Given a singly linked list, determine if it is a palindrome.     public class Solution {     public boolean isPalindrome(ListNode head) {         ListNode fast = head;         ListNode slow = head;         while (fast != null && fast.next != null) {             fast = fast.next.next;             slow = slow.next;          }         if (fast != null) {             slow = slow.next; //如1234321，则slow指向第二个3，如果是12344321则slow指向第二个4         }         slow = reverse(slow);//把321翻转成123         fast = head;//fast指向开头的1         while (slow != null) {             if (fast.val != slow.val) {                 return false;             }             fast = fast.next;             slow = slow.next;         }         return true;     }       public ListNode reverse(ListNode head) {         ListNode prev = null;         while (head != null){             ListNode next = head.next;                  head.next = prev;             prev = head;             head = next;         }         return prev;     } }

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