206. Reverse Linked List

反转链表：

/**
 * 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)
            return NULL;
        
        ListNode *p = (ListNode*)malloc(sizeof(ListNode));
        p->next = NULL;
        p->val=head->val;   //该处曾误写为ListNode *p=head; 致使debug花了许久时间    
        head=head->next;
        
        while(head!=NULL)
        {
            ListNode *temp=head->next; //save the next node of head
            
            head->next=p;
            p=head;
            
            head=temp;
        }
        return p;
    }
};