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#!/usr/bin/perl -s
use v5.24;
use Test2::V0;
use Math::Prime::Util qw(todigits vecprod);
use List::Util qw(uniqnum);
use List::Gen;
use experimental qw(signatures);
our ($tests, $examples, $help, $base, $len);
$base //= 10;
$len //= 3;
run_tests() if $tests || $examples; # does not return
die <<EOS if $help;
usage: $0 [-examples] [-tests] [-help] [-base=BASE] [-len=LEN]
-examples
run the examples from the challenge
-tests
run some tests
-base=BASE
find colorful numbers in base BASE. Default: 10
-len=LEN
find colorful number of length LEN (in base BASE). Default: 3
EOS
### Input and Output
gen_colorful($base, $len)->say;
### Implementation
# Build a generator for colorful numbers in base $base and length $len.
sub gen_colorful ($base, $len) {
my ($lower, $upper) = ($base**($len - 1), $base**$len - 1);
my $subsets = consecutive_subsets($len);
<$lower..$upper>->filter(sub {is_colorful($_, $subsets, $base)});
}
# Check if a given number is colorful in base $base. The "color" index
# subsets must be provided as the array ref $subsets. The subset's last
# element's length defines the length of the colorful numbers.
sub is_colorful ($n, $subsets, $base) {
my $len = $subsets->[-1]->@*;
@$subsets == scalar uniqnum map vecprod((todigits $n, $base, $len)[@$_]),
@$subsets;
}
# Generate an array of all consecutive subsets of indices 0 .. $len - 1.
sub consecutive_subsets ($len) {
my @index = (0 .. $len - 1);
my @res;
for my $l (1 .. $len) {
for my $i (0 .. $len - $l) {
push @res, [$i .. $i + $l - 1];
}
}
\@res;
}
### Examples and tests
sub run_tests {
SKIP: {
skip "examples" unless $examples;
is gen_colorful(10, 3)->apply, bag {item 263; etc}, 'example';
}
SKIP: {
skip "tests" unless $tests;
}
done_testing;
exit;
}
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