Leetcode 206. 反转链表

数据结构基础的头插法

代码如下：

/**
 * 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) {
        ListNode* _head = new ListNode;
        ListNode* cur;
        while(head!= nullptr){
            if(_head->next == nullptr){
                cur = head;
                head = head->next;
                cur->next = nullptr;
                _head->next = cur;                
            }else{
                cur = head;
                head = head->next;
                cur->next = _head->next;
                _head->next = cur;
            }
        }
        return _head->next;
    }
};