C++实现将一个字符串中的字符替换成另一个字符串的方法

本文实例讲述了C++实现将一个字符串中的字符替换成另一个字符串的方法，分享给大家供大家参考。具体方法如下：

题目要求：

原地实现字符串中的每个空格替换成"%20"，例如输入"Wearehappy"，输出"We%20are%20happy"
被替换的字符串当然不仅仅是空格，上面只是个例子
这是道很好的题目，也是百度面试中的一道题，题目不难，但是问题得考虑全面。这里给出如下实现代码：

#include<iostream>
#include<vector>
#include<cassert>

usingnamespacestd;

intfindNumberFirst(constchar*str,constchar*dest,vector<int>&pvec)
{
if(str==NULL||dest==NULL)
return0;

intpos=0;
intlenStr=strlen(str);
intlenDest=strlen(dest);

if(lenStr<lenDest)
return0;

intcount=0;
while(pos<=lenStr-lenDest)
{
if(strncmp(str+pos,dest,strlen(dest))==0)
{
pvec.push_back(pos);
pos+=lenDest;
count++;
}
else
{
pos++;
}
}

returncount;
}

intfindNumberLast(constchar*str,constchar*dest,vector<int>&pvec)
{
if(str==NULL||dest==NULL)
return0;

intstrLen=strlen(str);
intdestLen=strlen(dest);

if(strLen<destLen)
return0;

intpos=0;
while(pos<=strLen-destLen)
{
if(strncmp(str+pos,dest,strlen(dest))==0)
{
pos+=destLen;
pvec.push_back(pos-1);
}
else
{
pos++;
}

}

returnpvec.size();
}

voidreplaceArray(char*str,constchar*src,constchar*dest)
{
if(str==NULL||src==NULL||dest==NULL)
return;

vector<int>pvec;
intstrLen=strlen(str);
intsrcLen=strlen(src);
intdestLen=strlen(dest);

if(strLen<srcLen)
return;

intposBefore=0;
intposAfter=0;

if(srcLen<destLen)
{
intcount=findNumberLast(str,src,pvec);
if(count<=0)
return;

posAfter=strLen+count*(destLen-srcLen)-1;
posBefore=strLen-1;

while(count>0&&posBefore>=0)
{
if(pvec[count-1]==posBefore)
{
posAfter-=destLen;
strncpy(str+posAfter+1,dest,strlen(dest));
count--;
posBefore--;
}
else
{
str[posAfter--]=str[posBefore--];
}
}
}
elseif(strLen>destLen)
{
intcount=findNumberFirst(str,src,pvec);
if(count<=0)
return;

posAfter=0;
posBefore=0;

inti=0;
while(count>=0&&posBefore<strLen)
{
if(count>0&&pvec[i]==posBefore)
{
strncpy(str+posAfter,dest,strlen(dest));
posAfter+=destLen;
count--;
posBefore+=srcLen;
i++;
}
else
{
str[posAfter++]=str[posBefore++];
}
}
str[posAfter]="\0";
}
}

voidmain()
{
char*str=newchar[100];
if(str==NULL)
return;
memset(str,"\0",100);

constchar*src="";
constchar*dest="%20";
//case1:只有1个空格
strcpy(str,"");

replaceArray(str,src,dest);
cout<<"str:"<<str<<endl;

replaceArray(str,dest,src);
cout<<"str:"<<str<<endl;

//case2:两个空格
strcpy(str,"");

replaceArray(str,src,dest);
cout<<"str:"<<str<<endl;

replaceArray(str,dest,src);
cout<<"str:"<<str<<endl;

//case3:正常情况
strcpy(str,"wearehappy");

replaceArray(str,src,dest);
cout<<"str:"<<str<<endl;

replaceArray(str,dest,src);
cout<<"str:"<<str<<endl;

//case3:空格在前
strcpy(str,"wearehappy");

replaceArray(str,src,dest);
cout<<"str:"<<str<<endl;

replaceArray(str,dest,src);
cout<<"str:"<<str<<endl;

//case4:空格在后
strcpy(str,"wearehappy");

replaceArray(str,src,dest);
cout<<"str:"<<str<<endl;

replaceArray(str,dest,src);
cout<<"str:"<<str<<endl;

//case4:没空格
strcpy(str,"wearehappy");

replaceArray(str,src,dest);
cout<<"str:"<<str<<endl;

replaceArray(str,dest,src);
cout<<"str:"<<str<<endl;

//case5:两边一样
strcpy(str,"wearehappy");

replaceArray(str,src,dest);
cout<<"str:"<<str<<endl;

src="%20";
assert(dest=="%20");
replaceArray(str,dest,src);
cout<<"str:"<<str<<endl;
}

分析上述代码，很有意思的一个情况是srcLen和destLen或大或小的情形，其边界条件的判定不一样。比如wearehappy为例子，从后往前拷贝时，count=2。

在count=0时，恰好将最前面的空格替换完成，we则不用重复拷贝。但是对于从前往后拷贝，当count=0时，最后面的happy将不会被拷贝。

希望本文所述实例对大家C++程序算法设计的学习有所帮助。