面试题4：替换空格

知识点

C/C++中的每个字符串都以字符''作为结尾

为了节省内存，C/C++把常量字符串放到单独的一个内存区域，当几个指针赋值给相同的常量字符串，它们实际会指向相同的地址

    char str1[] = "hello";
    char str2[] = "hello";
    char *str3 = "hello";
    char *str4 = "hello";

char *指向的地址是相同的

数组是分配空间后再将内容拷贝到数组中的，指针直接指向常量字符串

面试题4

本题心得是从尾到头复制可以提高效率，其他字符串问题也可以考虑从尾到头复制

自己开始写的实现写成string[i] = ' '， 一定要注意==，另外本题是在原字符串上做替换

书中示例：

/*length 为字符数组string的总容量*/
void ReplaceBlank(char string[], int length)
{
    if(string == NULL && length <= 0)
        return;

    /*originalLength 为字符串string的实际长度*/
    int originalLength = 0;
    int numberOfBlank = 0;
    int i = 0;
    while(string[i] != '')
    {
        ++ originalLength;

        if(string[i] == ' ')
            ++ numberOfBlank;

        ++ i;
    }

    /*newLength 为把空格替换成'%20'之后的长度*/
    int newLength = originalLength + numberOfBlank * 2;
    if(newLength > length)
        return;

    int indexOfOriginal = originalLength;
    int indexOfNew = newLength;
    while(indexOfOriginal >= 0 && indexOfNew > indexOfOriginal)
    {
        if(string[indexOfOriginal] == ' ')
        {
            string[indexOfNew --] = '0';
            string[indexOfNew --] = '2';
            string[indexOfNew --] = '%';
        }
        else
        {
            string[indexOfNew --] = string[indexOfOriginal];
        }

        -- indexOfOriginal;
    }
}

 完整代码：

// ReplaceBlank.cpp : Defines the entry point for the console application.
//

// 《剑指Offer——名企面试官精讲典型编程题》代码
// 著作权所有者：何海涛

#include "stdafx.h"
#include <string>

/*length 为字符数组string的总容量*/
void ReplaceBlank(char string[], int length)
{
    if(string == NULL && length <= 0)
        return;

    /*originalLength 为字符串string的实际长度*/
    int originalLength = 0;
    int numberOfBlank = 0;
    int i = 0;
    while(string[i] != '')
    {
        ++ originalLength;

        if(string[i] == ' ')
            ++ numberOfBlank;

        ++ i;
    }

    /*newLength 为把空格替换成'%20'之后的长度*/
    int newLength = originalLength + numberOfBlank * 2;
    if(newLength > length)
        return;

    int indexOfOriginal = originalLength;
    int indexOfNew = newLength;
    while(indexOfOriginal >= 0 && indexOfNew > indexOfOriginal)
    {
        if(string[indexOfOriginal] == ' ')
        {
            string[indexOfNew --] = '0';
            string[indexOfNew --] = '2';
            string[indexOfNew --] = '%';
        }
        else
        {
            string[indexOfNew --] = string[indexOfOriginal];
        }

        -- indexOfOriginal;
    }
}

void Test(char* testName, char string[], int length, char expected[])
{
    if(testName != NULL)
        printf("%s begins: ", testName);

    ReplaceBlank(string, length);

    if(expected == NULL && string == NULL)
        printf("passed.
");
    else if(expected == NULL && string != NULL)
        printf("failed.
");
    else if(strcmp(string, expected) == 0)
        printf("passed.
");
    else
        printf("failed.
");
}

// 空格在句子中间
void Test1()
{
    const int length = 100;

    char string[length] = "hello world";
    Test("Test1", string, length, "hello%20world");
}

// 空格在句子开头
void Test2()
{
    const int length = 100;

    char string[length] = " helloworld";
    Test("Test2", string, length, "%20helloworld");
}

// 空格在句子末尾
void Test3()
{
    const int length = 100;

    char string[length] = "helloworld ";
    Test("Test3", string, length, "helloworld%20");
}

// 连续有两个空格
void Test4()
{
    const int length = 100;

    char string[length] = "hello  world";
    Test("Test4", string, length, "hello%20%20world");
}

// 传入NULL
void Test5()
{
    Test("Test5", NULL, 0, NULL);
}

// 传入内容为空的字符串
void Test6()
{
    const int length = 100;

    char string[length] = "";
    Test("Test6", string, length, "");
}

//传入内容为一个空格的字符串
void Test7()
{
    const int length = 100;

    char string[length] = " ";
    Test("Test7", string, length, "%20");
}

// 传入的字符串没有空格
void Test8()
{
    const int length = 100;

    char string[length] = "helloworld";
    Test("Test8", string, length, "helloworld");
}

// 传入的字符串全是空格
void Test9()
{
    const int length = 100;

    char string[length] = "   ";
    Test("Test9", string, length, "%20%20%20");
}

int _tmain(int argc, _TCHAR* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();
    Test6();
    Test7();
    Test8();
    Test9();

    return 0;
}