面试题24. 反转链表

题目：

 

 

解答：

/**
 * 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 (NULL == head || NULL == head->next)
        {
            return head;
        }

        ListNode *p1;
        ListNode *p2;
        ListNode *p3;

        p1 = head;
        p2 = head->next;
        while (p2 != NULL)
        {
            p3 = p2->next;
            p2->next = p1;
            p1 = p2;
            p2 = p3;
        }

        head->next = NULL;
        head = p1;

        return head;
    }
};