10.2-7 单链表的就地逆置

1 使用固定量的存储空间

2 主要思想是头插法,重复执行 “第二个元素插入到第一个元素之前，迭代第二个元素”

#include <iostream>
#include <crtdbg.h>
#include <cstring>
using namespace std;

typedef int DataType;
//建立链表
class list
{
private:
    struct Node
    {
        DataType data;
        Node* next;
    };
    Node *head;//哨兵位
public:
    list()
    {
        Init();
    }
    ~list()
    {
        Delete();
    }
    void Init();
    void Delete();
    void Insert(const DataType data);
    void Print();
    bool Empty()    { return head->next == NULL;}
    void ReversedSort(); //就地逆序
};
void list::Init()
{
    head = new Node;
    head->next = NULL;
}
void list::Delete()
{
    for(Node *p=head; p != NULL;)
    {
        Node *pTemp = p->next;
        delete p;
        p = pTemp;
    }
    head = NULL;
}
//头插法
void list::Insert(const DataType data)
{
    Node *pNew = new Node;
    pNew->data = data;
    pNew->next = head->next;
    head->next = pNew;
}
void list::Print()
{
    for (Node *p = head->next; p != NULL; p = p->next)
    {
        cout << p->data << endl;
    }
}
//就地逆序
void list::ReversedSort()
{
    Node *pOne = head->next;
    Node *pTwo = pOne->next;
    Node *pFirst = NULL;
    
    while(pOne != NULL)
    {
        // 第二项变第一项，第一项连接第三项
        pFirst = head->next;
        head ->next = pTwo;
        pOne->next = pTwo->next;
        pTwo->next = pFirst;

        if (pOne->next != NULL)
        {
            pTwo = pOne->next;
        }
        else
        {
            break;
        }
    }
}

int main() 
{ 
    //检测是否有内存泄露 需要加头文件#include <crtdbg.h>
    _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);

    list l;
    
    for (int i=10; i>0; --i)
    {
        l.Insert(i);
    }

    l.Print();

    l.ReversedSort();

    l.Print();

    system("pause");
    return 0; 
}