2015-10-18 10:42:52 +08:00

58 lines
1.4 KiB
C++

// Source : https://leetcode.com/problems/palindrome-linked-list/
// Author : Hao Chen
// Date : 2015-07-17
/**********************************************************************************
*
* 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?
*
**********************************************************************************/
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* findMiddle(ListNode* head) {
ListNode *p1=head, *p2=head;
while(p2 && p2->next){
p1 = p1->next;
p2 = p2->next->next;
}
return p1;
}
ListNode* reverseLink(ListNode* head) {
ListNode* p=NULL;
while (head) {
ListNode* q = head->next;
head->next = p;
p = head;
head = q;
}
return p;
}
bool isPalindrome(ListNode* head) {
ListNode* pMid = findMiddle(head);
ListNode* pRev = reverseLink(pMid);
for(;head!=pMid; head=head->next, pRev=pRev->next) {
if (head->val != pRev->val) {
return false;
}
}
return true;
}
};