题目描述

定义一个函数，输入一个链表的头结点，反转该链表并输出反转后链表的头结点。

样例

/*递归版本*/
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(!head || !head->next) return head;
        auto newHead = reverseList(head->next);
        head->next->next = head;
        head->next = NULL;
        return newHead;
    }
};

/*迭代版本*/
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(!head) return head;

        auto p = head,q = p->next;
        while(q)
        {
            auto tmp = q->next;
            q->next = p;
            p = q,q = tmp;
        }
        head->next = NULL;
        return p;
    }
};