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palindrome-linked-list

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Palindrome Linked List – LeetCode 234

Problem

Description

Given a singly linked list, determine if it is a palindrome.

Answer

Original

Code

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    bool isPalindrome(ListNode* head) {
        if(!head || !head->next) return true;
        
        ListNode *slow = head;
        ListNode *fast = head;
        while(fast && fast->next){
            slow = slow->next;
            fast = fast->next->next;
        }
        
        ListNode *curr = slow->next;
        slow->next = nullptr; //important!!!
        fast = curr? curr->next: nullptr;
        while(curr) {          
            curr->next = slow;
            slow = curr;
            curr = fast;
            fast = fast? fast->next: nullptr;   
        }
        
        while(slow){
            if(head->val == slow->val){
                head = head->next;
                slow = slow->next;
            } else 
                return false;
        }
        
        return true;
    }
};

思路

先是使用快慢双指针法找到中间节点，然后将后半部分翻转，再从头尾对应检验val的值。相当于之前几道题的一同考察，时间复杂度$O(n)$，空间复杂度$O(1)$。
耗时$19$ ms，排名$56.02\%$

Better

思路

还没看到更好的思路。