剑指offer——面试题5：替换空格

利用STL：

#include"iostream"
#include"stdio.h"
#include"algorithm"
using namespace std;

string ReplaceBlank(string src)
{
    if(src.find(" ")>src.length())
        return src;
    while(src.find(" ")<src.length())
    {
        int pos=src.find(" ");
        src=src.replace(pos,1,"%20");
    }
    return src;
}

void Test(char *testName,string testStr,string resStr)
{
    if(testName!=nullptr)
        printf("the %s begin：",testName);
    if(testStr=="")
    {
        printf("the source string is null!
");
        return;
    }
    string res=ReplaceBlank(testStr);
    if(res==resStr)
        printf("passed.
");
    else
        printf("failed
");
}

//包含空格的字符串
void Test1()
{
    Test("Test1","We are happy enough !","We%20are%20happy%20enough%20!");
}

//不包含空格的字符串
void Test2()
{
    Test("Test2","WeAreHappy","WeAreHappy");
}

//空字符串
void Test3()
{
    Test("Test3","","");
}

int main()
{
    Test1();
    Test2();
    Test3();
    return 0;
}

官方给出的O(n)复杂度的算法：

// 面试题5：替换空格
// 题目：请实现一个函数，把字符串中的每个空格替换成"%20"。例如输入“We are happy.”，
// 则输出“We%20are%20happy.”。

#include <cstdio>
#include <cstring>

/*length 为字符数组str的总容量，大于或等于字符串str的实际长度*/
void ReplaceBlank(char str[], int length)
{
    if(str == nullptr && length <= 0)
        return;

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

        if(str[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(str[indexOfOriginal] == ' ')
        {
            str[indexOfNew --] = '0';
            str[indexOfNew --] = '2';
            str[indexOfNew --] = '%';
        }
        else
        {
            str[indexOfNew --] = str[indexOfOriginal];
        }

        -- indexOfOriginal;
    }
}

// ====================测试代码====================
void Test(char* testName, char str[], int length, char expected[])
{
    if(testName != nullptr)
        printf("%s begins: ", testName);

    ReplaceBlank(str, length);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    return 0;
}