10585 - Center of symmetry

windows2k · Post by **windows2k** » Sat Dec 20, 2003 5:29 am

How to solve the problem?
I first thought matching every possible solution, O(n^2) , it must be TLE.
then I thought sorting by angle, still can't find any relation.
Could someone offer me a hint? Thx

Farid Ahmadov · Post by **Farid Ahmadov** » Sat Dec 20, 2003 10:08 am

You have to check just from one point to all other points if the center of mass lies between this points. If there is no such points then answer is no.

windows2k · Post by **windows2k** » Sat Dec 20, 2003 10:16 am

Farid Ahmadov wrote:You have to check just from one point to all other points if the center of mass lies between this points. If there is no such points then answer is no.

what do you mean?
I choose a point randomly, then find the center of mass lies on the other points?
@@~~

Per · Post by **Per** » Sun Dec 21, 2003 4:05 am

Hint: if the center of symmetry exists, then it is very easy to find.

Farid Ahmadov · Post by **Farid Ahmadov** » Sun Dec 21, 2003 12:37 pm

hint: Just find mass center. If its coords x and y are of form d.5 or d.0 then it can be center of symmetry.

Tomson · Post by **Tomson** » Sun Dec 21, 2003 5:54 pm

hint: you could sort all the points first of all.

diac_paul · Post by **diac_paul** » Fri Jan 21, 2005 2:10 am

I know how the solve the problem, at least i have the idea. the problem is that i have to use the function "atan2(y,x);" - that is in C. I must include "math.h", i know, i did that but i get complietion error. Please how can i use this function?.
Thanks.

little joey · Post by **little joey** » Fri Jan 21, 2005 10:12 am

You have to link it explicitly using the compiler switch "-lm".
If you are using gcc, the command would be:

Code: Select all

gcc -lm p10585.c

or something like that.

diac_paul · Post by **diac_paul** » Fri Jan 21, 2005 9:14 pm

I know about -lm, but how can I use this on the judge system? Can I put something like "-lm" at the "Comment" when i submit?
Thanks again.

little joey · Post by **little joey** » Sat Jan 22, 2005 9:41 am

The judge always compiles with this option, so you don't have to do anything.
If you get compilation error from the judge, it has nothing to do with including math.h, but maybe something else is wrong? Look at the reply sent back to you by the judge.

diac_paul · Post by **diac_paul** » Sat Jan 22, 2005 1:26 pm

Yes, i figured it out.... I was using M_PI witch should be the pi constant (it probably works only in borland C, or i dont't know...) . But
where do i see the "reply sent back to me by the judge"? . It just shows Compilation error.

little joey · Post by **little joey** » Sat Jan 22, 2005 2:52 pm

It depends on your personal settings. If you choose to let the judge send a reply to your email address, you'll get an email explaining the result, including the compiler output in case of compilation error. That can be quite helpful, especially if you don't use gcc.