字符串反转操作，网易的一道面试题

/**
*函数实现将网址进行如下操作
*www.google.com转成com.google.www 及mail.netease.com转成com.netease.mail
*
*不允许用STL,空间为0(1)
*
*C/C++ code
*
*void reverse(cha * ptr)
*{
*
*
*}
*
*
**/

char* find_next_right_dot(char *str)
{
if(str == NULL)
return NULL;

char * src = str; //save the source string address

while(*src) {
if(*src++ == '.' && *src != '.' && *src != '\0') {
//if the first char is dot and the follow char is not, and the string dont end with
//0, get the char address after the last dot.
return src;
}
}

return NULL;
}

int find_first_dot(char *str)
{
if(str == NULL)
return -1;
if(*str != '.')
return 0;
char *src = str;
while(*src) {
if(*src++ == '.' && *src != '.')
return (int)(src - str);
}

return 0;
}

void reverse(char *begin, char *end)
{
if(NULL == begin || end == NULL)
return;
char *tmp1 = begin;
char *tmp2 = end;
char a;

while(tmp2 > tmp1) {
a = *tmp1;
*tmp1++ = *(tmp2);
*tmp2-- = a;
}

}

void reverse_by_dot(char *str)
{
if(NULL == str)
return;

char *des = str;
int firstdot = find_first_dot(str);
des += firstdot;

while(1) {

if(*des++ == '.' && *des != '\0') {

char *tmp = str + firstdot;
char *dotstr = des - 2;//roll back to the char is not dot

reverse(tmp, dotstr); //reverse the string from tmp to dotstr

if(find_next_right_dot(dotstr)) {
des = find_next_right_dot(dotstr);
firstdot = des - str;
} else {
firstdot = des + 1 - str;
}
}

if(*des == '\0') { // has reached the end of string des

char *tmp = str + firstdot;
char *dotstr = des - 1;
reverse(tmp, dotstr);

break;
}

}
}

int main(void)
{
char *str = "neteasy.google.com";
printf("%s\n", str);
reverse(str, str + strlen(str) - 1);
printf("reverse: %s\n", str);
reverse_by_dot(str);
printf("reverse_by_dot: %s\n", str);

char *str1 = "...hello...world...";
printf("\n%s\n", str1);
reverse(str1, str1 + strlen(str1) - 1);
printf("reverse: %s\n", str1);
reverse_by_dot(str1);
printf("reverse_by_dot: %s\n", str1);

char *str2 = "hello world";
printf("\n%s\n", str2);
reverse(str2, str2 + strlen(str2) - 1);
printf("reverse: %s\n", str2);
reverse_by_dot(str2);
printf("reverse_by_dot: %s\n", str2);

return 0;
}