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#!/usr/bin/env perl
use strict;
use warnings;
use experimental qw{ say state postderef signatures };
my @examples = (
[ [ 2, 1 ], [ 2, 3 ], [ 2, 5 ] ],
[ [ 1, 4 ], [ 3, 4 ], [ 10, 4 ] ],
[ [ 0, 0 ], [ 1, 1 ], [ 2, 3 ] ],
[ [ 1, 1 ], [ 1, 1 ], [ 1, 1 ] ],
[ [ 1000000, 1000000 ], [ 2000000, 2000000 ], [ 3000000, 3000000 ] ],
);
for my $input (@examples) {
my $output = straight_line( $input->@* );
my $str = join ',', map { qq{[$_]} } map { join ', ', $_->@* } $input->@*;
say <<"END";
Input: \@str = ($str)
Output: $output
END
}
sub straight_line (@array) {
my %angles;
for my $i ( 0 .. $#array ) {
my $k = $array[$i];
for my $j ( $i + 1, $#array ) {
next unless $i != $j;
next unless defined $array[$j];
my $l = $array[$j];
my $a1 = find_angle( $k, $l );
my $a2 = find_angle( $l, $k );
$angles{$a1} = 1;
$angles{$a2} = 1;
}
}
return scalar keys %angles <= 2 ? 'true' : 'false';
}
sub find_angle ( $p1, $p2 ) {
return
# sprintf '%.06f',
atan2( $p1->[1] - $p2->[1], $p1->[0] - $p2->[0] );
}
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