替换空格

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.”。

思路: 首先准备两个指针：p1和p2。p1指向原始字符串的末尾，p2指向替换之后的字符串的末尾。接下来我们向前移动p1，逐个把它指向的字符串复制到p2指向的位置，知道遇到第一个空格为止。此时p1向前移动一格，在p2之前插入字符串”%20”，同时p2向前移动三格。

I		a
		p1(indexofOriginal)		p2(indexofNew)
I				a
	p1		p2
I	%	2	0	a
p1,p2

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

void ReplaceBlank(char str[], int length)
{
    if(str == nullptr || length <= 0)
        return ;

    int OriginalLength = 0;
    int numberofBlank = 0;
    int i = 0;

    while(str[i] != '\0')
    {
        ++OriginalLength;
        if(str[i] == ' ')
            ++numberofBlank;
        ++i;
    }

    int newLength = OriginalLength + numberofBlank * 2;
    if(newLength > length)
        return ;

    int indexofOriginal = OriginalLength;     //p1
    int indexofNew = newLength;               //p2

    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. \n");
    else if(expected == nullptr && str != nullptr)
        printf("Failed. \n");
    else if(strcmp(str, expected) == 0)
        printf("Passed. \n");
    else
        printf("Failed. \n");
}

//空格在句子中间
void Test1()
{
    const int length = 50;

    char str[length] = "hello world";
    Test("test1", str, length, "hello%20world");
}

// 空格在句子开头
void Test2()
{
    const int length = 50;

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

// 空格在句子末尾
void Test3()
{
    const int length = 50;

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

// 连续有两个空格
void Test4()
{
    const int length = 50;

    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 = 50;

    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 = 50;

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

// 传入的字符串没有空格
void Test8()
{
    const int length = 50;

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

// 传入的字符串全是空格
void Test9()
{
    const int length = 50;

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

int main()
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();
    Test6();
    Test7();
    Test8();
    Test9();

    return 0;
}