Solution to task 1

1 files changed, 69 insertions, 0 deletions

diff --git a/challenge-218/jo-37/perl/ch-1.pl b/challenge-218/jo-37/perl/ch-1.pl
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+++ b/challenge-218/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -s
+
+use v5.24;
+use Test2::V0;
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV >= 3;
+usage: $0 [-examples] [-tests] [--] [N...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+N...
+    list of at least three numbers
+
+EOS
+
+
+### Input and Output
+
+say max_prod(@ARGV);
+
+
+### Implementation
+
+# There are only two candidates for the maximum product of three
+# elements:
+# - the product of the three largest elements
+# - the product of the two smallest elements with the largest
+sub max_prod {
+    # For the sake of convenience, sort the elements.
+    my @s = sort {$a <=> $b} @_;
+    my $left = $s[0] * $s[1] * $s[-1];
+    my $right = $s[-3] * $s[-2] * $s[-1];
+
+    $left > $right ? $left : $right;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is max_prod(3, 1, 2), 6, 'example 1';
+        is max_prod(4, 1, 3, 2), 24, 'example 2';
+        is max_prod(-1, 0, 1, 3, 1), 3, 'example 3';
+        is max_prod(-8, 2, -9, 0, -4, 3), 216, 'example 4';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is max_prod(-1, -2, -3, -4, -5), -6, 'all negative';
+        is max_prod(1, 2, 3, 4, -5), 24, 'one negative';
+        is max_prod(1, 2, -3, -4, 4, 5), 60, 'left wins';
+        is max_prod(1, -2, 3, -4, 4, 5), 60, 'right wins';
+	}
+
+    done_testing;
+    exit;
+}