Leetcode 234. Palindrome Linked List Link list

234. Palindrome Linked List

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

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

Main topic:

Determine whether a single-linked list is a palindrome list.

Ideas:

Find the nodes in the middle of the list, divide the list from the middle into 2 parts, the right half to reverse the list, and then compare the left half with the inverted right-half list. to produce results.

/** * definition for singly-linked list. * struct listnode {  *     int val; *     ListNode *next;  *     listnode (int x)  : val (x),  next (NULL)  {} *  }; */class solution {public:    listnode * reverselist ( Listnode *head)  //chain list reversal     {         listnode *pre,*next;        pre = null;         next = NULL;                 while (head)         {             next = head->next;             head->next = pre;             pre = head;             head = next;        }         return pre;    }    bool ispalindrome ( Listnode* head)  {        if ( NULL == head  | |  null == head->next)              return true;        int len = 0;         ListNode *p = head;         while (P)         {             len++;            p = p->next;         }        listnode  * rightListHead;                 rightListHead = head;        int  leftlen = len / 2;        int rightlen =  len - leftLen;        int i = leftLen;         while (i)         {             rightListHead =  rightlisthead->next;            i--;         } &nBsp;      rightlisthead = reverselist (RightListHead);                 listnode * left  = head;        ListNode * right =  rightlisthead;                 while (I < leftlen)         {             if (Left->val == right->val)              {                 left = left->next;                 right = right->next;             }            else             {                 return false;             }            i ++;        }        return  true;    }};

Reviewed the method of single-linked list inversion.

2016-08-12 20:17:23

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Leetcode 234. Palindrome Linked List Link list