题解 | #反转链表#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
#include <iostream>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    ListNode* ReverseList(ListNode* head) {
        // write code here
        if(head){
            ListNode *p = head;
        ListNode *q = p->next;
        
        while (q) {
            ListNode *r = q;
            q = q -> next;
            r -> next = p;
            p = r;
        }
        head -> next = nullptr;
        head = p;

        }
        
        return head;
    }
};