Horizontally Visible Segments
Time Limit: 10 Seconds
Memory Limit: 32768 KB
There is a number of disjoint vertical line segments in the plane. We say that
two segments are horizontally visible if they can be connected by a horizontal
line segment that does not have any common points with other vertical segments.
Three different vertical segments are said to form a triangle of segments if
each two of them are horizontally visible. How many triangles can be found in
a given set of vertical segments?
Write a program which for each data set:
reads the description of a set of vertical segments,
computes the number of triangles in this set,
writes the result.
The first line of the input contains exactly one positive integer d equal to
the number of data sets, 1 <= d <= 20. The data sets follow.
The first line of each data set contains exactly one integer n, 1 <= n <=
8 000, equal to the number of vertical line segments.
Each of the following n lines consists of exactly 3 nonnegative integers separated
by single spaces:
yi', yi'', xi - y-coordinate of the beginning of a segment, y-coordinate of
its end and its x-coordinate, respectively. The coordinates satisfy 0 <=
yi' < yi'' <= 8 000, 0 <= xi <= 8 000. The segments are disjoint.
The output should consist of exactly d lines, one line for each data set. Line
i should contain exactly one integer equal to the number of triangles in the
i-th data set.
0 4 4
0 3 1
3 4 2
0 2 2
0 2 3
Source: Central Europe 2001