Solution to task 2

1 files changed, 76 insertions, 0 deletions

diff --git a/challenge-141/jo-37/perl/ch-2.pl b/challenge-141/jo-37/perl/ch-2.pl
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+++ b/challenge-141/jo-37/perl/ch-2.pl
@@ -0,0 +1,76 @@
+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use Math::Prime::Util qw(todigits fromdigits);
+use List::MoreUtils 'indexes';
+use experimental 'signatures';
+
+our ($tests, $examples, $verbose);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [-verbose] [M N]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+-verbose
+    print the found numbers instead of the count thereof
+
+M N
+    find integers created by M divisible by N
+
+EOS
+
+
+### Input and Output
+
+main: {
+    my @like_num = like_num(@ARGV);
+    say $verbose ? "@like_num" : scalar @like_num;
+}
+
+
+### Implementation
+
+# Take the indices of 1-bits in the binary representation of the numbers
+# from 1 to 2 ** length($m) - 2 (representing all valid subsequences) as
+# slice arguments for the decimal digits of $m and collect all results
+# divisible by $n.  Return the found unique numbers.
+sub like_num ($m, $n) {
+    my @digits = todigits $m;
+    my %divisible;
+    @divisible{
+        grep !($_ % $n),
+        map fromdigits([@digits[indexes {$_} todigits $_, 2, @digits]]),
+        1 .. 2 ** @digits - 2
+    } = ();
+
+    keys %divisible;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+        is scalar(like_num(1234, 2)), 9, 'example 1';
+        is scalar(like_num(768, 4)), 3, 'example 2';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+        is scalar(like_num(135, 2)), 0, 'no even subnumber';
+        is scalar(like_num(12345, 1)), 2**5 - 2, 'count valid subnumbers';
+        is scalar(like_num(2222, 2)), 3, 'count numbers only once';
+	}
+
+    done_testing;
+    exit;
+}