Abstract Classes - Polymorphism

内容：

说明：

特定数量键值对，超过数量，最后的替换最开始的

示例代码：

// AbstractClasses-Polymorphism.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <string>
#include <map>
#include <iostream>
using namespace std;

struct Node
{
    Node* next;
    Node* prev;
    int value;
    int key;
    Node( Node* p, Node* n, int k, int val ) : prev( p ), next( n ), key( k ), value( val ) {};
    Node( int k, int val ) : prev( NULL ), next( NULL ), key( k ), value( val ) {};
};

class Cache
{

protected:
    map<int, Node*> mp; //map the key to the node in the linked list
    int cp;  //capacity
    Node* tail; // double linked list tail pointer
    Node* head; // double linked list head pointer
    virtual void set( int, int ) = 0; //set function
    virtual int get( int ) = 0; //get function

};

class LRUCache : public Cache
{
public:

    //the max size in map
    LRUCache( int num )
    {
        this->cp = num;
        tail = NULL;
        head = NULL;
    }
    void set( int key, int value )
    {
        //first key
        if( head == NULL )
        {
            mp[key] = new Node( key, value );
            head = mp[key];
            tail = head;
        }
        else
        {
            //over the size,pre instead oldest
            if( mp.size() >= this->cp )
            {
                Node* cur = tail->prev;
                int dKey = tail->key;
                mp.erase( dKey );
                tail = cur;
            }
            //insert
            else
            {
                mp[key] = new Node( NULL, tail, key, value );
                head = mp[key];
                head->next->prev = head;
            }
        }

    }
    int get( int key )
    {
        if( mp.find( key ) != mp.end() )
        {
            return mp[key]->value;
        }
        else
        {
            return -1;
        }
    }
private:

};

//by zhaocl
int main()
{
    int n, m;
    cin >> n >> m;
    LRUCache  mc( m );

    for( int i = 0; i < n; i++ )
    {
        string cmd;
        cin >> cmd;

        if( !cmd.compare( "get" ) )
        {
            int key;
            cin >> key;
            cout << mc.get( key ) << endl;
        }
        else if( !cmd.compare( "set" ) )
        {
            int key, value;
            cin >> key >> value;
            mc.set( key, value );
        }
    }

    system( "pause" );
    return 0;
}

知识点：

1、多态的简单应用：名字相同、参数不同

2、纯虚函数的实现