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#!/usr/bin/env perl
#===============================================================================
#
# FILE: 10102.pl
#
# USAGE: ./10102.pl x1 y1 x2 y2 x3 y3
#
# DESCRIPTION: Check if point (0, 0) lies within given triangle
# Output 1 if it is inside (including on the line),
# 0 otherwise
#
# REQUIREMENTS: List::Util (Core module)
# AUTHOR: Pete Houston (pete), cpan@openstrike.co.uk
# ORGANIZATION: Openstrike
# VERSION: 1.0
# CREATED: 22/02/21
#===============================================================================
use strict;
use warnings;
use List::Util 'pairs';
my @vertices = map { /([0-9.-]+)/ and $1 } @ARGV;
die "Usage: $0 x1 y1 x2 y2 x3 y3\n" unless 6 == @vertices;
my $result = inside_paths (@vertices);
print "$result\n";
sub inside_paths {
# Determine if the origin is on the same side of each line segment
# as the 3rd point. If so, it is inside. If it is on any of the line
# segments that's a positive result right away.
# Return 1 for inside or on the line, 0 otherwise
my @p = pairs @_;
my $sameside = 0;
for my $i (0 .. 2) {
my @q = map { $p[$_] } grep { $_ != $i } (0 .. 2);
my $dx = $q[1]->[0] - $q[0]->[0];
my $dy = $q[1]->[1] - $q[0]->[1];
my $originside = (0 - $q[0]->[1]) * $dx -
(0 - $q[0]->[0]) * $dy;
return 1 if $originside == 0; # On the line
my $cornerside = ($p[$i]->[1] - $q[0]->[1]) * $dx -
($p[$i]->[0] - $q[0]->[0]) * $dy;
$sameside++ unless ($originside > 0 xor $cornerside > 0);
}
return $sameside == 3 ? 1 : 0;
}
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