利用字符出现的次数，编写一个方法，实现基本的字符串压缩功能。

利用字符出现的次数，编写一个方法，实现基本的字符串压缩功能。比如，字符串为aabccccaaa，会变为a2b1c5a3.若“压缩”后的字符串没有变短，则返回原先的字符串。

1.使用stringstream将int转化为string

2

string (1)	string& append (const string& str);
substring (2)	string& append (const string& str, size_t subpos, size_t sublen);
c-string (3)	string& append (const char* s);
buffer (4)	string& append (const char* s, size_t n);
fill (5)	string& append (size_t n, char c);
range (6)	template <class InputIterator> string& append (InputIterator first, InputIterator last);
initializer list(7)	string& append (initializer_list<char> il);

3.

std::string::push_back

void push_back (char c);

Append character to string
Appends character c to the end of the string, increasing its length by
one.

string StringCompress(const string &s)
{
string retStr;
if(s.length() == 0)
return retStr;
char tmpChar = s.at(0);
int charCount = 0;
for(string::const_iterator it = s.begin();it != s.end();it++)
{
if(*it ==tmpChar)
{
charCount++;
}
else
{
retStr.push_back(tmpChar);

//使用stringstream将int转化为string
stringstream ss;
ss<<charCount;
string tmpStr = ss.str();

retStr.append(tmpStr);
tmpChar = *it;
charCount = 1;
}

if (it == s.end()-1)
{
retStr.push_back(tmpChar);
//使用stringstream将int转化为string
stringstream ss;
ss<<charCount;
string tmpStr = ss.str();

retStr.append(tmpStr);
}

}

if (retStr.length()<s.length())
{
return retStr;
}
else
{
return s;
}
}