#include <iostream>
#include <string.h>
 
void reverse( char *s )
{
    if ( !s )
        return;
 
    char *e = s + strlen( s ) - 1;
    while ( s < e )
    {
        *e ^= *s;
        *s ^= *e;
        *e-- ^= *s++;
    }
}
int main() {
	// your code goes here
	char* s1 = "123";
	char* s2 = "";
 
	std::cout << s1 << " - " << std::endl;
	reverse(s1);
	std::cout << s1 << std::endl;
 
	std::cout << s2 << " - " << std::endl;
	reverse(s2);
	std::cout << s2 << std::endl;
	return 0;
}

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