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”

• 思路
  先计算所有空格数，然后按照所有空格数的数量实现计算出最后一个字符所在位置，再从后往前遍历用两个指针复制字符，如果遇到空格就将代替字符写入，直到两个指针相等。

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

void ReplaceBlank(char *string, unsigned int length)
{
if (string == nullptr || length < 1)
return;

int i = 0;
unsigned int blankCount = 0;
unsigned int originalLength = 0;
while (string[i]!='\0')
{
originalLength++;
if (string[i] == ' ')
blankCount++;
i++;
}
unsigned newLength = originalLength + blankCount*2;
if (newLength > length)
return;

int indexOfNew = newLength;
int indexOfOriginal = originalLength;

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