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#!/usr/bin/perl -s
use v5.24;
use Test2::V0;
use autodie;
use List::UtilsBy qw(count_by nmax_by);
use experimental qw(signatures refaliasing);
our ($solve, $examples, $verbose);
run_tests() if $solve || $examples; # does not return
die <<EOS unless @ARGV;
usage: $0 [-examples] [-solve] [FILE]
-examples
run the examples from the challenge
-solve
solve the task
FILE
filename containing text to be decoded. Use '-' for STDIN
EOS
### Input and Output
say decode(\*ARGV);
### Implementation
# Taking the most frequent character at each position.
sub decode ($fh) {
# Read matrix
my @words;
while (<$fh>) {
push @words, [split /\s+/, $_];
}
# Transpose matrix
my @pos = map {
\my $p = \$_;
[map $words[$_][$p], 0 .. $#words]
} 0 .. $words[0]->$#*;
# Find the frequency of characters at each position and select the
# most frequent.
my $decrypt;
for my $pos (@pos) {
my %freq = count_by {$_} @$pos;
$decrypt .= nmax_by {$freq{$_}} keys %freq;
}
$decrypt;
}
### Examples and tests
sub run_tests {
SKIP: {
skip "examples" unless $examples;
my $data = <<'EOD';
H x l 4 !
c e - l o
z e 6 l g
H W l v R
q 9 m # o
EOD
open my $fh, '<', \$data;
is decode($fh), 'Hello', 'Example';
}
SKIP: {
skip "solve" unless $solve;
my $data = <<'EOD';
P + 2 l ! a t o
1 e 8 0 R $ 4 u
5 - r ] + a > /
P x w l b 3 k \
2 e 3 5 R 8 y u
< ! r ^ ( ) k 0
EOD
open my $fh, '<', \$data;
say decode($fh);
}
done_testing;
exit;
}
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