反转一个链表

Class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* tmp;
        ListNode* cur = head;
        ListNode* pre = nullptr;
        while (cur) {
            tmp = cur->next; 
            cur->next = pre; 
            
            //更新pre和cur指针
            pre = cur;
            cur = tmp;
        }
        return pre; 
    }
};