【手撕】翻转链表

#include<iostream>

using namespace std;

struct ListNode
{
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(nullptr) { }
};

class Solution
{
public:
    ListNode* reverseList(ListNode* head)
    {
        if (head == nullptr || head->next == nullptr)
        {
            return head;
        }
        ListNode* cur = head;
        ListNode* pre = nullptr;
        while (cur != nullptr)
        {
            ListNode* next = cur->next;
            cur->next = pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }
};

int main()
{
    ListNode* node1 = new ListNode(1);
    ListNode* node2 = new ListNode(2);
    ListNode* node3 = new ListNode(3);
    ListNode* node4 = new ListNode(4);
    node1->next = node2;
    node2->next = node3;
    node3->next = node4;
    ListNode* head = node1;
    ListNode* cur = node1;

    cout << "翻转之前的链表为：";
    while (cur != nullptr)
    {
        cout << cur->val <<"->";
        cur = cur->next;
    }
    cout << "nullptr" << endl;

    Solution solution;
    cur = solution.reverseList(head);

    cout << "翻转之后的链表为：";
    while (cur != nullptr)
    {
        cout << cur->val << "->";
        cur = cur->next;
    }
    cout << "nullptr" << endl;

    return 0;
}