[Leetcode]234.palindrome Linked List

Topic

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

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

Ideas

Using the double pointer method to find the midpoint position of the linked list, the elements after the midpoint of the list (excluding the midpoint element) are flipped and then matched to the previous element one by one of the midpoint position of the linked list.

Code

/ *---------------------------------------* Date: 2015-07-18* sjf0115* title: 234.Palindrome Linked list* website: https:// leetcode.com/problems/palindrome-linked-list/* Result: ac* Source: leetcode* Blog:-----------------------------------------*/ #include <iostream>#include <Vector>using namespace std;struct listnode{int val; ListNode*Next ListNode (int x): Val (x), Next (NULL) {}};class Solution { Public: BOOL Ispalindrome (ListNode*Head) {if(Head==nullptr) {return true; }//if        //Midpoint positionListNode*Slow=Head ListNode*Fast=Head -Next while(Fast&&Fast -Next) {Slow=Slow -Next Fast=Fast -Next -Next }//whileSlow=Slow -Next//FlipListNode*Q=Reverselist (slow);//Determine if it is a palindrome stringListNode*P=Head while(p&&Q) {if(p -Val!=Q -Val) {return false; }//ifP=P -Next Q=Q -Next }//while        return true; }Private://FlipListNode*Reverselist (ListNode*Head) {if(Head==nullptr) {returnHead }//if        //Head nodeListNode*Dummy= NewListNode (-1); ListNode*P=Head ListNode*NextNode=P -Next while(p) {NextNode=P -Next P -Next=Dummy -Next Dummy -Next=P P=NextNode; }//while        returnDummy -Next    }};int Main () {solution S; ListNode*Head= NewListNode (1); ListNode*Node2= NewListNode (2); ListNode*Node3= NewListNode (3); ListNode*Node4= NewListNode (4); ListNode*Node5= NewListNode (3); ListNode*Node6= NewListNode (2); ListNode*Node7= NewListNode (1); Head -Next=Node2; Node2 -Next=Node3; Node3 -Next=Node4; Node4 -Next=NODE5; Node5 -Next=Node6; Node6 -Next=Node7; BOOL Result=S.Ispalindrome (head);if(Result) {cout<<"It's a palindrome."<<Endl }//if    Else{cout<<"Not a palindrome."<<Endl }//else    return 0;}

Run time

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[Leetcode]234.palindrome Linked List