剑指Offer - 面试题24. 反转链表（遍历/递归）

示例:
输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL
 
限制：
0 <= 节点个数 <= 5000

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
    	if(!head)
    		return head;
        ListNode *prev = NULL, *nt = head->next;
        while(head && head->next)
        {
        	head->next = prev;
        	prev = head;
        	head = nt;
        	nt = nt->next;
        }
        head->next = prev;
        return head;
    }
};

class Solution {
    ListNode *newhead;
public:
    ListNode* reverseList(ListNode* head) {
        if(!head || !head->next)
            return head;
        ListNode *newHead = reverseList(head->next);
        head->next->next = head;//head->next下一个的next指向前面head
        head->next = NULL;//避免循环链表
        return newHead;//每层都返回最后一个节点，新的头
    }
};