On Sat, Mar 24, 2012 at 11:45 AM, =D0=A0=D0= =BE=D0=BC=D0=B0=D0=BD =D0=A2=D0=BA=D0=B0=D0=BB=D0=B5=D0=BD=D0=BA=D0=BE <rain.roman@gmail.= com> wrote:

#works for 3.55 mins
P =3D 295075153
o1 =3D 210205= 973
o2 =3D 22795300
(0 .. P).each do | i |
= =C2=A0 =C2=A0 if i ^ (i ^ o1) =3D=3D o1 and ((i * 2 + 5) % P) ^ (((i ^ o1) = * 3 + 7) % P) =3D=3D o2

=C2=A0 =C2=A0 =C2=A0 =C2=A0 puts i
=C2=A0 =C2=A0 =C2=A0 =C2= =A0 break
=C2=A0 =C2=A0 end
end
Code written = in C gives me the solution in only 2 seconds. I suppose that it's calle= d not by ruby slowlyness, but my shitty coding abilities. Cuold tou please = tell me the weaknesse of the code?

It's not shitty coding (though I do f= ind your code unreadable). It's because C is compiled into assembly, wh= en you tell it to iterate that many times, it can put the number directly i= nto a register and decrement the value. Ruby is much higher level than that= . Numbers are actual objects that must be allocated, for example. So an exa= mple like this, C is going to dramatically outperform Ruby.

Like anything, there are tradeoffs. For instance, by represe= nting numbers with just binary values that fit into C's int type, you y= our program up to the limitations of that type (e.g. in Ruby you can have a= rbitrarily large numbers `$ruby -e 'p 2**2000'`).

And, of course, the Ruby version uses a closure. ANSI C= doesn't have closures, which prevents it from being able to support ve= ry powerful coding styles (i.e. many of the things Lisp is famous for).

So, really its best to figure out what your domain is a= nd find a language well suited to that. If your domain is hardcore number c= runching, then Ruby is probably not the best choice (though I did solve a n= umber of Project Euler problems with it).

-Josh

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