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main.cpp
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/// Source : https://leetcode.com/problems/palindrome-linked-list/description/
/// Author : liuyubobobo
/// Time : 2018-05-10
#include <iostream>
using namespace std;
/// Definition for singly-linked list.
struct ListNode {
int val;
ListNode *next;
ListNode(int x) : val(x), next(NULL) {}
};
/// Two Pointers to Reverse and Traverse
/// Time Complexity: O(n)
/// Space Complexity: O(1)
class Solution {
public:
bool isPalindrome(ListNode* head) {
if(head == NULL || head->next == NULL)
return true;
ListNode* slow = head;
ListNode* fast = head;
while(fast->next != NULL && fast->next->next != NULL){
slow = slow->next;
fast = fast->next->next;
}
slow->next = reverse(slow->next);
slow = slow->next;
ListNode* cur = head;
while(slow != NULL){
if(cur->val != slow->val)
return false;
else{
slow = slow->next;
cur = cur->next;
}
}
return true;
}
private:
ListNode* reverse(ListNode* head){
if(head == NULL || head->next == NULL)
return head;
ListNode* pre = head;
ListNode* cur = head->next;
ListNode* next = cur->next;
head->next = NULL;
while(true){
cur->next = pre;
pre = cur;
cur = next;
if(cur == NULL)
break;
next = cur->next;
}
return pre;
}
};
int main() {
return 0;
}