LeetCode-234. 回文链表

LeetCode-234. 回文链表

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isPalindrome(ListNode head) {
        if(head==null || head.next==null){
            return true;
        }
        // 根据快慢指针，找到链表的中点
        ListNode fast = head;
        ListNode slow = head;
        while(fast.next!=null && fast.next.next!=null){
            fast = fast.next.next;
            slow = slow.next;
        }
        slow = reverse(slow.next);
        while(slow!=null){
            if(head.val != slow.val){
                return false;
            }
            head=head.next;
            slow=slow.next;
        }
        return true;
    }

    private ListNode reverse(ListNode head){
        ListNode pre=null;
        while(head!=null){
             ListNode tmp = head.next;
             head.next=pre;
             pre = head;
             head = tmp;
        }
        return pre;
    }
}