leetcode 234 Palindrome Linked List（难易度：Easy）

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Palindrome Linked List

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?

代码：

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     struct ListNode *next; * }; */struct ListNode *reverseList(struct ListNode *head);bool isPalindrome(struct ListNode* head) {if (head == NULL || head->next == NULL)//如果只有一个节点，则是回文串return true;struct ListNode *slow = head;struct ListNode *fast = head;while (fast->next != NULL && fast->next->next != NULL)//fast既不是尾节点也不是倒数第二个节点{slow = slow->next;//慢指针走一步fast = fast->next->next;//快指针走两步}slow = slow->next;struct ListNode *head2 = reverseList(slow);struct ListNode *head1 = head;while (head2 != NULL) {if (head2->val != head1->val)return false;head1 = head1->next;head2 = head2->next;}return true;}struct ListNode *reverseList(struct ListNode *head) {struct ListNode *pre = NULL;struct ListNode *next = NULL;while (head != NULL) {next = head->next;head->next = pre;pre = head;head = next;}return pre;}

原题地址：https://leetcode.com/problems/palindrome-linked-list/

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