现代程序设计 homework-09

本次作业要求:

1. 了解Lambda的用法

计算“Hello World!”中

a.字母‘e’的个数

b. 字母‘l’的个数

 

2. 练习使用智能指针

  打印“Hello World!”循环右移n位的结果

  Example:

    n = 1, output = “!Hello World”

  n = 3, output = “ld!Hello Wor”

这次作业比较简单,也没有什么好说的，

第一个采用Lambda表达式确实比较方便,

只要这样一行代码就可以搞定

cnt=count_if(str.cbegin(),str.cend(),[=](char tempCh){return tempCh==ch;});

第二个关于数组的循环移位问题,<编程之美>中已经有不错的介绍,这里要求用智能指针实现,反而觉得有些画蛇添足的感觉

unique_ptr<string>p(new string(str));
    for(int i=0;i<k;i++)
    {
        char ch=(*p)[n-1];
        for(int j=n-1;j>0;j--)
        {
            (*p)[j]=(*p)[j-1];
        }
        (*p)[0]=ch;
    }
    cout<<*p<<endl;

当然可以用O(n)的算法去实现循环移位

void MyRightShiftStr::RightShift()
{
    k%=n;
    ReverseStr(0,n-k-1);
    ReverseStr(n-k,n-1);
    ReverseStr(0,n-1);
}
void MyRightShiftStr::ReverseStr(int left,int right)
{
    for( ;left<right;left++,right--)
    {
        char temp=str[right];
        str[right]=str[left];
        str[left]=temp;
    }
}

封装好的完整代码如下:

// homework-09.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<string>
#include<vector>
#include<memory>
#include<algorithm>
using namespace std;
class MyRightShiftStr
{
public:
    MyRightShiftStr();
    ~MyRightShiftStr();
    bool GetString();
    bool GetK();
    void PrintResult();
    void ReverseStr(int left,int right);
    void RightShift();
    void UptrShift();
private:
    string str;
    int k;
    int n;
};


MyRightShiftStr::MyRightShiftStr()
{
}

MyRightShiftStr::~MyRightShiftStr()
{
}
bool MyRightShiftStr::GetString()
{
    cout<<"Please input the str you want to RightShift: "<<endl;
    try
    {
        if(getline(cin,str)==nullptr)
        {
            throw("Input Error");
        }
    }
    catch(char *ExceptionStr)
    {
        cout<<"Exception: "<<ExceptionStr<<endl;
        return false;
    }
    n=str.length();
}
bool MyRightShiftStr::GetK()
{
    cout<<"Please input the K: "<<endl;
    try
    {
        if(scanf_s("%d",&k)!=1)
        {
            throw("Input Error");
        }
    }
    catch(char *ExceptionStr)
    {
        cout<<"Exception: "<<ExceptionStr<<endl;
        return false;
    }
    if(k<0)
    {
        k=n+k%n;
    }
}
void MyRightShiftStr::UptrShift()
{
    unique_ptr<string>p(new string(str));
    for(int i=0;i<k;i++)
    {
        char ch=(*p)[n-1];
        for(int j=n-1;j>0;j--)
        {
            (*p)[j]=(*p)[j-1];
        }
        (*p)[0]=ch;
    }
    cout<<*p<<endl;
}
void MyRightShiftStr::RightShift()
{
    k%=n;
    ReverseStr(0,n-k-1);
    ReverseStr(n-k,n-1);
    ReverseStr(0,n-1);
}
void MyRightShiftStr::ReverseStr(int left,int right)
{
    for( ;left<right;left++,right--)
    {
        char temp=str[right];
        str[right]=str[left];
        str[left]=temp;
    }
}
void MyRightShiftStr::PrintResult()
{
    cout<<"The str after RightShift: "<<endl;
    cout<<str<<endl;
}

class MyCountStr
{
public:
    MyCountStr();
    ~MyCountStr();
    bool GetString();
    bool GetChar();
    void CountLambda();

private:
    string str;
    char ch;
    int cnt;
};

MyCountStr::MyCountStr()
{
}

MyCountStr::~MyCountStr()
{
}

bool MyCountStr::GetString()
{
    cout<<"Please input the str you want to Count: "<<endl;
    try
    {
        if(getline(cin,str)==nullptr)
        {
            throw("Input Error");
        }
    }
    catch(char *ExceptionStr)
    {
        cout<<"Exception: "<<ExceptionStr<<endl;
        return false;
    }
}

bool MyCountStr::GetChar()
{
    cout<<"Please input the char you want to Count: "<<endl;
    try
    {
        if((ch=getc(stdin))==NULL)
        {
            throw("Input Error");
        }
    }
    catch(char *ExceptionStr)
    {
        cout<<"Exception: "<<ExceptionStr<<endl;
        return false;
    }
}

void MyCountStr::CountLambda()
{
    cnt=count_if(str.cbegin(),str.cend(),[=](char tempCh){return tempCh==ch;});
    cout<<"The num of "<<ch<<" is "<<cnt<<endl;
}


int _tmain(int argc, _TCHAR* argv[])
{
    while(true)
    {
        MyCountStr myCS=MyCountStr::MyCountStr();
        if(!myCS.GetString())
        {
            continue;
        }
        if(!myCS.GetChar())
        {
            continue;
        }
        myCS.CountLambda();
        myCS.~MyCountStr();
        break;
    }
    while(true)
    {
        MyRightShiftStr myRSS=MyRightShiftStr::MyRightShiftStr();
        if(!myRSS.GetString())
        {
            continue;
        }
        if(!myRSS.GetK())
        {
            continue;
        }
        myRSS.RightShift();
        myRSS.PrintResult();
//        myRSS.UptrShift();
        myRSS.~MyRightShiftStr();
        break;
    }
    return 0;
}

运行截图如下：