题目

把字符串中出现的空格替换为“%20”。示例“Hello World” 变为“Hello%20World"

#include <stdio.h>
#include <string.h>

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

    //原始字符串的长度
    int originalLength = 0;
    int numberOfBlank = 0;
    int i = 0;
    while(string[i] != '\0')
    {
        ++originalLength;

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

        ++i;
    }


    //转换后字符串长度
    int newLength = originalLength + (numberOfBlank <<1);
    if(newLength > length)
        return;
    //从后向前复制
    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;
    }
}

//==========测试代码========
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.\n");
    else if(expected == NULL && string != NULL)
        printf("failed.\n");
    else if(strcmp(string, expected) == 0)
        printf("passed.\n");
    else
        printf("failed.\n");
}

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

    return 0;
}

结果：

QQ截图20160626202350.png

思考

合并两个数组（字符串）时，如果从前向后复制，需要重复移动的次数较多，那么可尝试从后向前复制，这样能减少移动的次数。