題目

把字符串中出現的空格替換為“%20”。示例“Hello World” 變為“Hello%20World"

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

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

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

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

        ++i;
    }


    //轉換后字符串長度
    int newLength = originalLength + (numberOfBlank <<1);
    if(newLength > length)
        return;
    //從后向前復制
    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;
    }
}

//==========測試代碼========
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");
}

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

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

// 空格在句子開頭
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");
}

// 連續有兩個空格
void Test4()
{
    const int length = 100;

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

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

// 傳入內容為空的字符串
void Test6()
{
    const int length = 100;

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

//傳入內容為一個空格的字符串
void Test7()
{
    const int length = 100;

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

// 傳入的字符串沒有空格
void Test8()
{
    const int length = 100;

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

// 傳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;
}

結果：

QQ截圖20160626202350.png

思考

合并兩個數組（字符串）時，如果從前向后復制，需要重復移動的次數較多，那么可嘗試從后向前復制，這樣能減少移動的次數。