I think this test should break some AC solutions:

443 -39 457 33
386 -773 561 127

Correct answer is -1, but I think some AC solutions can print 0

1. Use integer calculation for judging if the answer is -1 or 0.
2. Use integer calculation until the last step for the area (an integer-division).
3. Use 'long long' instead of 'long' or 'int'.

Also, here are some cases which might help.

0 0 -1000 0
0 0 1000 1
1000001000.000000

-1000 0 0 1000
0 -1000 1000 -999
2002004004.004004

0 400 1000 1000
-1000 -1000 355 -187
-1

0 400 1000 1000
-1000 -1000 350 -190
0

0 400 1000 1000
-1000 -1000 353 -188
16931680400.000000

-1000 -1000 1000 1000
-1000 -1000 1000 999
31984004000.000000

-1000 -1000 1000 1000
-472 -851 379 1
5800420000.000000

Since input numbers are integers, pseudovector product absolute value will be at least 1 if they aren't parallel, so you can compare it to 0.5 to have bigger margin for double precision error.

Edited by author 16.06.2021 15:21

Edited by author 16.06.2021 15:22

The geo looks simple. But fail at WA#10. :(


oops. Stupid error =)

Edited by author 29.11.2014 13:03

443 -39 457 33
386 -773 561 127

Correct answer: -1

check your solution for this case:

0 0 1 0
0 1 1 1

answer is -1.

what answer for this test:
0 0 1 0
1 1 2 1

0
or
-1
?

each window light travels in both directions, or one?

Don't use int. Use long long.

Edited by author 31.10.2012 15:46