Many times my code was reviewed and rewatched, but still WA7.
Could anybody help? What wrong with code? May be this algorithm gives not the optimal path?

int main()
{
    double r, a;
    std::cin >> r >> a;
    // first, walk to the edge of the island
    double s = r;
    // total angle of undiscovered edge
    const double a_left = 360.0 - 2.0*a;
    // hops count on 2*a "arc" line
    const int full_hops = (int)(a_left / (2.0*a));
    s += range(r, to_rad(2.0*a)) * full_hops;
    // remaining angle to hop
    double a_rem = a_left - full_hops * (2.0 * a);
    s += range(r, to_rad(a_rem));
    std::cout << std::fixed << std::setprecision(12) << s << std::endl;
}

Your algorithm allows me to AC.
Maybe problem in calculations, in "to_rad" or "range"...

I wrote to_rad and range to compile your code, and compared my code with yours: all output is identical. So, maybe you've mistook in one of these functions.

Edited by author 18.10.2009 00:00

Thank you a lot for a great advice!

Problem was eliminated after rewriting range() function:
Old: used cosinus theorem
New: using sinus to radius multiplication

AC!

Dmitriy S. Hodyrev!

You solved 1726. If you read this, help me, please.
My e-mail in my profile.

Moders, sorry for the message concerning not this problem. But did you think about a functionality of allowing users to send private messages to the other users' e-mails through a web-form?

I had the same problem: Since the cosine can be quite close to zero its square root is not calculated properly. So I also didn't use cosine theorem but calculated the length of the chords with simpler geometry:

long double x = radius * cos(angle);
long double y = radius * sin(angle);
long double ans = sqrt((x - radius) * (x - radius) + y * y);

Here the square root is done over the distance, not over the cosine, which, as it seems, solved the problem.

Use the law of sines instead of cosines.