From d320b17585f75191dcb9b9c94fcf0b217bf654d2 Mon Sep 17 00:00:00 2001
From: Jörg Sommrey <28217714+jo-37@users.noreply.github.com>
Date: Wed, 5 Jul 2023 22:05:43 +0200
Subject: Solution to task 2

---
 challenge-224/jo-37/perl/ch-2.pl | 94 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100755 challenge-224/jo-37/perl/ch-2.pl

diff --git a/challenge-224/jo-37/perl/ch-2.pl b/challenge-224/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..e9fe9f88e8
--- /dev/null
+++ b/challenge-224/jo-37/perl/ch-2.pl
@@ -0,0 +1,94 @@
+#!/usr/bin/perl -s
+
+use v5.24;
+use Test2::V0;
+use experimental 'signatures';
+
+our ($tests, $examples, $verbose);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV == 1 && length $ARGV[0] > 2;
+usage: $0 [-examples] [-tests] [-verbose] [STR]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+-verbose
+    show the found additive sequence instead of a true / false result
+
+STR
+    a string of decimal digits having a minimum length of three
+
+EOS
+
+
+### Input and Output
+
+say $verbose ?
+    "(@{is_additive(@ARGV) // []})" :
+    is_additive(@ARGV) ? 'true' : 'false';
+
+
+### Implementation
+
+# The task states: "An additive number is a string whose digits can form
+# an additive sequence."  I see some ambiguity in the phrase "digits can
+# form an additive sequence".  What is the meaning of "form"?  We might
+# pick arbitrary digits to build numbers.  However, the examples suggest
+# that we shall split the given string to get the numbers.  As this
+# interpretation significantly simplifies the task, I'll follow it.
+#
+# The first two numbers may be chosen freely from the head of the
+# string.  However, there are restrictions to their lengths: 
+# - The maximum length of the first number must leave enough room for a
+#   second number of length one and a tail of the same length as the
+#   first number.
+# - The maximum length of the second number must leave enough room for a
+#   tail of the lengths of both, the first and the second number.
+# Starting with all starting pairs conforming to above restrictions, we
+# check if the remaining string follows the additive sequence generated
+# by the starting pair.  Collecting the additive sequence along the way.
+
+sub is_additive ($s) {
+    my $l = length $s;
+    for (my $lx = 1; 2 * $lx + 1 <= $l; $lx++) {
+        for (my $ly = 1; 2 * $lx + $ly <= $l && $lx + 2 * $ly <= $l;  $ly++) {
+            my $x = substr $s, 0, $lx;
+            my $y = substr $s, $lx, $ly;
+            my $z = $x + $y;
+            my @seq = ($x, $y);
+            ($x, $y, $z) = ($y, $z, $y + $z, push @seq, $z)
+                while $s =~ /\G$x(?=$y$z)/gc; # set "pos" between x and y
+            return \@seq if $s =~ /\G$x$y$/g;
+        }
+    }
+    undef;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is is_additive(112358), [qw(1 1 2 3 5 8)], 'example 1';
+        ok !is_additive(12345), 'example 2';
+        is is_additive(199100199), [qw(1 99 100 199)], 'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is is_additive(11112111311152228), [qw(1111 2 1113 1115 2228)],
+            'a bit longer';
+        is is_additive('011'), [qw(0 1 1)], 'leading zero';
+	}
+
+    done_testing;
+    exit;
+}
-- 
cgit