leetcode——206——Reverse Linked List

Reverse a singly linked list.

/**
 * 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) {  
        if(head == NULL || head->next == NULL)  
            return head;  
              
        if(head->next->next == NULL)  
        {  
            ListNode* newhead = head->next;  
            newhead->next = head;  
            head->next = NULL;  
            return newhead;  
        }  
              
        ListNode* Prev = head;  
        ListNode* pNode = head->next; 
        Prev->next = NULL;
        ListNode* pTail = pNode->next;  
          
        while(pNode->next!=NULL)  
        {  
            pNode ->next = Prev;  
            Prev = pNode;  
            pNode = pTail;  
            pTail = pTail->next;  
              
              
        }  
        pNode ->next = Prev;  
        return pNode;  
          
          
    }  
};