剑指offer——面试题5：替换空格

利用STL：

 #include"iostream"
 #include"stdio.h"
 #include"algorithm"
 using namespace std;

 string ReplaceBlank(string src)
 {
     if(src.find(" ")>src.length())
         return src;
     while(src.find(" ")<src.length())
     {
         int pos=src.find(" ");
         src=src.replace(pos,,"%20");
     }
     return src;
 }

 void Test(char *testName,string testStr,string resStr)
 {
     if(testName!=nullptr)
         printf("the %s begin：",testName);
     if(testStr=="")
     {
         printf("the source string is null!\n");
         return;
     }
     string res=ReplaceBlank(testStr);
     if(res==resStr)
         printf("passed.\n");
     else
         printf("failed\n");
 }

 //包含空格的字符串
 void Test1()
 {
     Test("Test1","We are happy enough !","We%20are%20happy%20enough%20!");
 }

 //不包含空格的字符串
 void Test2()
 {
     Test("Test2","WeAreHappy","WeAreHappy");
 }

 //空字符串
 void Test3()
 {
     Test("Test3","","");
 }

 int main()
 {
     Test1();
     Test2();
     Test3();
     return ;
 }

官方给出的O(n)复杂度的算法：

 // 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 <= )
         return;

     /*originalLength 为字符串str的实际长度*/
     int originalLength = ;
     int numberOfBlank = ;
     int i = ;
     while(str[i] != '\0')
     {
         ++ originalLength;

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

         ++ i;
     }

     /*newLength 为把空格替换成'%20'之后的长度*/
     int newLength = originalLength + numberOfBlank * ;
     if(newLength > length)
         return;

     int indexOfOriginal = originalLength;
     int indexOfNew = newLength;
     while(indexOfOriginal >=  && indexOfNew > indexOfOriginal)
     {
         if(str[indexOfOriginal] == ' ')
         {
             str[indexOfNew --] = '';
             str[indexOfNew --] = '';
             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) == )
         printf("passed.\n");
     else
         printf("failed.\n");
 }

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

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

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

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

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

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

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

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

 // 传入nullptr
 void Test5()
 {
     Test("Test5", nullptr, , nullptr);
 }

 // 传入内容为空的字符串
 void Test6()
 {
     const int length = ;

     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 = ;

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

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

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

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

     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 ;
 }