leetcode-0234 Palindrome Linked List

Given the head of a singly linked list, return true if it is a palindrome.

Example 1:

Input: head = [1,2,2,1]
Output: true
Example 2:

Input: head = [1,2]
Output: false

Constraints:

The number of nodes in the list is in the range [1, 105].
0 <= Node.val <= 9

Follow up: Could you do it in O(n) time and O(1) space?

来源：力扣（LeetCode）
链接：https://leetcode.cn/problems/palindrome-linked-list

/**
 * 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) {
        ListNode fast = head, slow = head;
        while(fast != null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;
        }
        /* if this list has odd number of nodes */
        if(fast != null){
            slow = slow.next;
        }
        slow = reverseList(slow);
        fast = head;

        while(slow != null){
            if(slow.val != fast.val){
                return false;
            }
            slow = slow.next;
            fast = fast.next;
        }
        return true;
    }

    public ListNode reverseList(ListNode head){
        ListNode preNode = null;
        ListNode currNode = head;
        while(currNode != null){
            ListNode nextNode = currNode.next;
            currNode.next = preNode;
            preNode = currNode;
            currNode = nextNode;
        }
        return preNode;
    }
}

标签：head,Palindrome,ListNode,val,List,fast,next,slow,Linked
来源： https://www.cnblogs.com/chenjo/p/16278707.html