Solution to task 2

1 files changed, 83 insertions, 0 deletions

diff --git a/challenge-245/jo-37/perl/ch-2.pl b/challenge-245/jo-37/perl/ch-2.pl
new file mode 100755
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+++ b/challenge-245/jo-37/perl/ch-2.pl
@@ -0,0 +1,83 @@
+#!/usr/bin/perl -s
+
+use v5.24;
+use Test2::V0;
+
+our ($tests, $examples, $verbose);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [D...]
+
+-examples
+    run the examples from the challenge
+
+-tests
+    run some tests
+
+D...
+    list of decimal digits
+
+EOS
+
+
+### Input and Output
+
+say largest_of_three(@ARGV);
+
+
+### Implementation
+
+sub largest_of_three {
+	my (@digits, @ind, $mod) = sort @_;
+    for (0 .. $#digits) {
+        # The digit modulo 3
+        my $digit = $digits[$_] % 3;
+        # Store indices of digits that are not a multiple of 3
+        push $ind[$digit - 1]->@*, $_ if $digit;
+        # Update the digit sum
+        $mod += $digit;
+    }
+    $mod %= 3;
+    # Delete the fewest smallest digits to obtain a digit sum divisible
+    # by 3.
+    delete @digits[
+        !$mod-- ? () : $ind[$mod] ? $ind[$mod][0] : $ind[!$mod]->@[0, 1]
+    ];
+
+    # Build the maximum number from the remaining digits in descending
+    # order or fail.
+    @digits ? 0 + join '', reverse grep defined, @digits : -1;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is largest_of_three(8, 1, 9), 981, 'example 1';;
+        is largest_of_three(8, 6, 7, 1, 0), 8760, 'example 2';
+        is largest_of_three(1), -1, 'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is largest_of_three(6, 4, 3), 63, 'single 1 mod 3';
+        is largest_of_three(6, 5, 3), 63, 'single 2 mod 3';
+        is largest_of_three(6, 4, 4, 3), 63, 'double 1 mod 3';
+        is largest_of_three(6, 5, 5, 3), 63, 'double 2 mod 3';
+        is largest_of_three(6, 3), 63, '0 mod 3';
+        is largest_of_three(1, 1), -1, 'double 1';
+        is largest_of_three(2, 2), -1, 'double 2';
+        is largest_of_three(2), -1, 'like example 3';
+        is largest_of_three(0, 0, 0, 1), 0, 'zero';
+        is largest_of_three(6, 2, 2, 2, 7), 6222, 'remove the largest digit';
+	}
+
+    done_testing;
+    exit;
+}