LeetCode 206. 反转链表

示例:

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

/**
 * 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) {
        ListNode *prevNode = NULL, *nextNode;
        while(head)
        {
            nextNode = head->next;
            head->next = prevNode;
            prevNode = head;
            head = nextNode;
        }
        return prevNode;
    }
};

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
    if (head == NULL || head->next == NULL)
        return head;
    ListNode *p = reverseList(head->next);
    head->next->next = head;	//p->next = head;错误写法
    head->next = NULL;
    return p;
    }
};