234. Palindrome Linked List

Posted 2020-08-31 copperface

• Total Accepted: 88244
• Total Submissions: 277193
• Difficulty: Easy
• Contributors: Admin

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

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

来源： https://leetcode.com/problems/palindrome-linked-list/?tab=Description

分析

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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 == NULL || head->next == NULL) return true;                   //use slow and fast pointer to find the mid node         ListNode* slow = head, * fast = head;         while(fast && fast->next && fast->next->next){             slow = slow->next;             fast = fast->next->next;         }                   //reverse the right half list         ListNode* l1 = head;         ListNode* l2 = slow->next;         slow->next = NULL;         l2 = reverse(l2);                   //compare the two lists‘s node vale         while(l2){             if(l1->val != l2->val) return false;             l1 = l1->next;             l2 = l2->next;         }                   return true;     }           ListNode* reverse(ListNode* head){         ListNode* pre = NULL;         ListNode* cur = head;         while(cur){             ListNode* tmp = cur->next;             cur->next = pre;             pre = cur;             cur = tmp;         }         return pre;     } };

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