【100题】左旋转字符串-----整体翻转+局部再次翻转

//使用两次翻转的方法来对付左旋转字符串
//即----字符串的循环左移

#include <iostream>
using namespace std;

void ReverseString(char *pStart,char *pEnd)
{
	if(pStart != NULL || pEnd != NULL)
	{
		while(pStart <= pEnd)
		{
			swap(*pStart,*pEnd);
			pStart++;
			pEnd--;
		}
	}
}

char *LeftRotateString(char *p,unsigned int n)
{
	if(p != NULL)
	{
		int nLength = static_cast<int> (strlen(p));
		if(nLength>0 || n>=0 && n <= nLength)
		{
			char *pFirstStart = p;
			char *pFirstEnd = p+n-1;
			char *pSecondStart = p+n;
			char *pSecondEnd = p+nLength-1;
			
			ReverseString(pFirstStart,pFirstEnd);
			ReverseString(pSecondStart,pSecondEnd);
			ReverseString(pFirstStart,pSecondEnd);
		}
	}
	return p;
}

void main()
{
	char str[] = "abcdefg";
	cout << LeftRotateString(str,4) <<endl;
}