Solution to task 2

1 files changed, 73 insertions, 0 deletions

diff --git a/challenge-119/jo-37/perl/ch-2.pl b/challenge-119/jo-37/perl/ch-2.pl
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+++ b/challenge-119/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use Math::Cartesian::Product;
+use experimental qw(signatures postderef);
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [N ...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+N ...
+    Find the N-th element of the "CY sequence"
+
+EOS
+
+
+### Input and Output
+
+say cy($_) for @ARGV;
+
+
+### Implementation
+
+# Find the n-th element of the CY sequence.
+sub cy ($n) {
+    # CY sequence known so far.
+    state @cy;
+    # Current number of digits.
+    state $digits;
+
+    # Augment the calculated CY sequence by blocks having an increasing
+    # number of digits if the requested element isn't in the list yet.
+    local $" = '';
+    push @cy,
+        cartesian {"@_" !~ /11/} ([1 .. 3]) x ++$digits
+        while $n > @cy;
+
+    # Join the digits of the n-th element.
+    "$cy[$n - 1]->@*";
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is cy(5), 13, 'example 1';
+        is cy(10), 32, 'example 2';
+        is cy(60), 2223, 'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is cy(11), 33, 'last 2-digit element';
+        is cy(12), 121, 'first 3-digit element';
+	}
+
+    done_testing;
+    exit;
+}