[数据结构与算法]回文链表java实现

/**
 * 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) {
        //首先判断如果链表为空或者只有一个元素
        if(head == null || head.next == null){
            return true;
        }
        //分割链表
        //快慢指针，需要注意的是当总数为奇数
        ListNode slow = head;
        ListNode fast = slow.next;
        while(fast.next != null && fast.next.next != null){
            slow = slow.next;
            fast = fast.next.next;
        }
        //检查是否为奇数
        ListNode half = slow.next;
        if(fast.next != null){
            half = half.next;
        }
        //反转后半部分链表，逐个比对素直接返回
        half = reverse(half);
        while(half != null){
            if(head.val != half.val){
                return false;
            }
            half= half.next;
            head = head.next;
        }
        return true;
    }

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