LeetCode 206. 反转链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        //翻转head开头的链表，返回新链表的头节点
        if(!head||!head->next)   return head;
        ListNode* p=reverseList(head->next);
        head->next->next=head;
        head->next=NULL;
        return p;
    }
};