2014
02-13

# 3D Camera

Long long ago, there was a world of triangles. A smart guy in that world invented a camera, whose viewfinder was a
triangle. The camera’s visual range could be represented by three RAYS. As the figure shows, the camera’s visual
range could be represented by three rays OA, OB, OC. Note that the visual range is INFINITE.

Now, we have a camera with known visual range and a triangle DEF in the space. The inventor wants to know if the
camera can see the triangle, in other words, if there is at least one point of the triangle strict in the visual range.

The input consists of multiple test cases. The first line of input contains an integer T, which is the number of test cases.

The first line of each test case contains 12 integers: Ox, Oy, Oz, Ax, Ay, Az, Bx, By, Bz, Cx, Cy, Cz. The second line
contains 9 integers: Dx, Dy, Dz, Ex, Ey, Ez, Fx, Fy, Fz.
All the integers in a line are separated by a whitespace.

[Technical Specification]
T is an integer, and T <= 1000.
The input guaranteed that if you look from O, three points ABC are always arranged counterclockwise.
All integers EXCEPT T is in the range of [-100,100].
We guarantee the camera and the triangle are not degenerate.

The input consists of multiple test cases. The first line of input contains an integer T, which is the number of test cases.

The first line of each test case contains 12 integers: Ox, Oy, Oz, Ax, Ay, Az, Bx, By, Bz, Cx, Cy, Cz. The second line
contains 9 integers: Dx, Dy, Dz, Ex, Ey, Ez, Fx, Fy, Fz.
All the integers in a line are separated by a whitespace.

[Technical Specification]
T is an integer, and T <= 1000.
The input guaranteed that if you look from O, three points ABC are always arranged counterclockwise.
All integers EXCEPT T is in the range of [-100,100].
We guarantee the camera and the triangle are not degenerate.

2
90 -14 -17 71 98 94 69 59 -16 -52 68 13
-69 -96 43 81 -67 -79 66 -51 -53
0 0 1 0 0 0 1 0 0 0 1 0
0 0 -5 0 0 -6 1 1 -6

NO
YES

1. 我还有个问题想请教一下，就是感觉对于新手来说，递归理解起来有些困难，不知有没有什么好的方法或者什么好的建议？