面试题5：替换空格

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.”。

C++版本

//==================================================================
// 《剑指Offer——名企面试官精讲典型编程题》代码
// 作者：何海涛
//==================================================================

// 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;
}

Java版本

import java.util.Scanner;

public class Num_5 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scanner = new Scanner(System.in);
		String string = scanner.nextLine();
		char[] str = new char[100];
		for (int i = 0; i < string.length(); i++) {
			str[i] = string.charAt(i);
		}
		replaceBlank(str, string.length());
		scanner.close();
	}

	public static void replaceBlank(char[] str, int length) {

		if (str == null)
			return;

		int m = length;
		int n = length;
		// 先計算有多少個空格
		for (int i = 0; i < length; i++) {
			if (str[i] == ' ') {
				m += 2;
			}
		}

		m--;
		n--;

		while (n != m) {
			// 當沒有遇到空格
			if (str[n] != ' ') {
				str[m--] = str[n--];
			} else {
				n--;
				str[m--] = '0';
				str[m--] = '2';
				str[m--] = '%';
			}
		}
		System.out.println(str);
	}

}