根据输入偏移 旋转字符串

要求 

根据输入的字符串和偏移进行旋转

比如输入

"abcdefg" 0

获得"abcdefg"

输入"abcdefg" 2

获得fgabcde

#include <string>
#include <iostream>

using namespace std;

string Reverse(string& s, size_t begin, size_t end)
{
if (begin >= s.size() ||
end >= s.size())
return s;

while (begin < end)
{
char tmp = s[begin];
s[begin] = s[end];
s[end] = tmp;
begin++;
end--;
}
return s;
}

string RotateString(string s, int offset)
{
if (s.empty() || offset > s.size())
return s;

int length = s.size();
Reverse(s,0,length-offset-1);
Reverse(s, length - offset ,length-1);
Reverse(s,0,length-1);

return s;
}

关键在这几步的处理

Reverse(s,0,length-offset-1);
Reverse(s, length - offset ,length-1);
Reverse(s,0,length-1);

假设输入 "abcdefg" 0

实际上就是一下三步变换

1 edcba   fg

2 edcba gf

3 上一步字符串 整个的倒转

变成 fgabcde 达到目的