58 lines
1.4 KiB
C++
58 lines
1.4 KiB
C++
// Source : https://leetcode.com/problems/palindrome-linked-list/
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// Author : Hao Chen
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// Date : 2015-07-17
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/**********************************************************************************
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*
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* Given a singly linked list, determine if it is a palindrome.
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*
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* Follow up:
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* Could you do it in O(n) time and O(1) space?
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*
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**********************************************************************************/
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/**
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* Definition for singly-linked list.
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* struct ListNode {
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* int val;
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* ListNode *next;
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* ListNode(int x) : val(x), next(NULL) {}
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* };
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*/
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class Solution {
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public:
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ListNode* findMiddle(ListNode* head) {
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ListNode *p1=head, *p2=head;
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while(p2 && p2->next){
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p1 = p1->next;
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p2 = p2->next->next;
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}
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return p1;
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}
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ListNode* reverseLink(ListNode* head) {
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ListNode* p=NULL;
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while (head) {
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ListNode* q = head->next;
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head->next = p;
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p = head;
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head = q;
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}
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return p;
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}
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bool isPalindrome(ListNode* head) {
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ListNode* pMid = findMiddle(head);
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ListNode* pRev = reverseLink(pMid);
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for(;head!=pMid; head=head->next, pRev=pRev->next) {
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if (head->val != pRev->val) {
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return false;
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}
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}
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return true;
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}
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};
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