Solution to task 2

1 files changed, 72 insertions, 0 deletions

diff --git a/challenge-115/jo-37/perl/ch-2.pl b/challenge-115/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..56d3609563
--- /dev/null
+++ b/challenge-115/jo-37/perl/ch-2.pl
@@ -0,0 +1,72 @@
+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use List::MoreUtils 'lastidx';
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [-verbose] [d...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+d...
+    Digits to build the largest even number from.
+
+EOS
+
+
+### Input and Output
+
+say largest_even(@ARGV);
+
+
+### Implementation
+
+sub largest_even {
+    # Sort digits descending.
+    my @d = sort {$b <=> $a} @_;
+
+    # Some zeros don't make a number.
+    return if $#d && !$d[0];
+
+    # Get the index of the smallest even digit.
+    my $sei = lastidx {!($_ % 2)} @d;
+
+    # Give up if none found.
+	return if $sei < 0;
+
+    # Reorder the digits to form the largest even number.
+    join '', @d[0 .. $sei - 1, $sei + 1 .. $#d, $sei];
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is largest_even(1, 0, 2, 6), 6210, 'example 1';
+        is largest_even(1, 4, 2, 8), 8412, 'example 2';
+        is largest_even(4, 1, 7, 6), 7614, 'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is largest_even(1, 3, 5, 7), U(), 'no even digit';
+        is largest_even(0, 0), U(), 'multiple zeros only';
+        is largest_even(0), 0, 'single zero';
+	}
+
+    done_testing;
+    exit;
+}