I used ternary search for this problem
limits
-50000:50000  leads to wa18
-100000:100000 got wa1
-90000:90000 was AC

is there a normal solution without finding such segment?

What is the test 18? I really don't understand it... I wrote solution with ternary search, and I think that there is problem with accuracy of calculations. Have anybody this problem?

P.S. Sorry for my bad english :)

I have WA, but I don't guess at the feature of this test. Does anyone have a problem with this test? Please comment your trick.

There exist a closed form for the answer. hence the solution is O(K).

Pay attention that the algorithm is used only the function has some specific property.
But unfortunately, the property does not always exist.
So why do you take the algorithm for granted?

Try to check return values of trigonometric routines. For example, if you use atan2, make sure that if returned angle is negative you take an absolute value of it (not just add 2 * PI).

Good luck!

Can someone give me test number 5 and if possible write the solution?
Thank you.

EDIT: It also will be helpful if someone give me some tests with solutions and maybe some "tricky" test.

EDIT2: Got AC.

Edited by author 13.05.2008 03:18

Edited by author 15.05.2008 16:13

My solutions based on the wrong assumption that the view angle has only one maximum on abscissa axis (and with some tricks regarding to range of search or partition method in ternary search) pass all tests. Seems that more tests needed.

In other words, is for input {A, B, C, D} result always equal to result for input {C, D, A, B} ?

My programm search the greatest angle in x in [x1..x2] and got AC.
But it's wrong. For example in test 0 3 1 1.

PS Maybe i'm wrong

Edited by author 13.01.2011 21:20

I don't keep much hope on somebody looking in the discussion section for this problem with all that time passed after it's introduction but I would like to make the note that the view point  should be with non-negative x coordinate. This is not clear from the problem statement. I still haven't passed the whole problem but adding this logic to my solution upgraded me from wa8 to wa9. Any other tricks someone has noticed?

I've compared my computer with my friend's accepted program.
I found that his main algorithm is to find the maximal viewing angle between (x1,0) and (x2,0) using binary search.

But I have a random data like this
"-41 328 150 467"
my program output 0.528878 {which meet the peak value at (173.423285,0) on the right side of (x2,0)}
but his program output 0.527316 {which meet the peak value at (150,0)}

Must the programmer view the Billboard bewteen (x1,0) and (x2,0)?

If I misunderstood the description of this problem,please tell me the right one.

Thank you very much.

Please, give me test#6 or answer for test#6,or tell me what could be a problem?

Can anybody tell me what is correct answer for this test, please?
Test is:
-1000
-1000
1000
1

Edited by author 12.05.2008 21:15

Plz help i got WA on test #6. Can you give me some tests?

Edited by author 13.05.2008 20:38

Hi!
My math solution is absolute correct! I know that test #6 is:
-1000 -1000
1000 1
(Bin Search rulez :-))))

The correct answer on it is
3.141593

my program give this answer, but got WA. WHY??? It is impossible!!!

Help me please...

Bye!

how can i see whats test #5?
can anyone post me if he knows
pls

The test set for the problem awhile does not contain case (x1=x2 and y1*y2=0). For this case answer is PI/2, while all other cases y1*y2<=0 have answer PI.

The test case credits: Igor E. Tuphanov.