// 将一个长度为n的字符串向左循环移动m位,如:hello,world向左移动3位就变成了lo,worldhel
// 思路:把字符串切成长为m和n-m的两半,先分别对两部分进行逆序,最后对整个字符串逆序。

#include <iostream>
using namespace std;


void ReverseString(char * const str, const int count);

void RotateLeft(char *str, int num);

int _tmain(int argc, char *argv[])
{
    char str[] = "hello,world";

    RotateLeft(str, 3);

    cout << str << endl;

    getchar();
    return 0;
}

void ReverseString(char * const str, const int count)
{
    if (str == NULL || count < 2)
    {
        return;
    }

    char *start = str;
    char *end = str + count - 1;
    char tmp;

    while (end > start)
    {
        tmp = *end;
        *end = *start;
        *start = tmp;

        start++;
        end--;
    }
}

void RotateLeft(char *str, int num)
{
    if (str == NULL || num < 1)
    {
        return;
    }

    int length = (int)strlen(str);

    num = (num + length) % length;

    char *left = str;
    char *right = str + num;

    ReverseString(left, num);
    ReverseString(right, length - num);
    ReverseString(str, length);
}