From d8fae692ac658a6812c803605b83c650188fccbc Mon Sep 17 00:00:00 2001
From: Jörg Sommrey <28217714+jo-37@users.noreply.github.com>
Date: Mon, 30 Aug 2021 11:51:57 +0200
Subject: Solution to task 2

---
 challenge-128/jo-37/perl/ch-2.pl | 79 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100755 challenge-128/jo-37/perl/ch-2.pl

diff --git a/challenge-128/jo-37/perl/ch-2.pl b/challenge-128/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..62f101d10b
--- /dev/null
+++ b/challenge-128/jo-37/perl/ch-2.pl
@@ -0,0 +1,79 @@
+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use List::Util 'reduce';
+use experimental 'signatures';
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [arrivals departures]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+arrivals
+    comma and/or space separated list of arrivals, e.g.
+    '11:20, 14:30'
+
+departures
+    comma and/or space separated list of departures, e.g.
+    '11:50, 15:00'
+
+EOS
+
+
+### Input and Output
+
+say platforms(map [split /[,\s]\s*/, $_], @ARGV);
+
+
+### Implementation
+
+# Unwinding from behind and outwards:
+# - Convert the arrival and departure arrays to AoAs holding the time
+#   and train delta (arrivals: +1, departures: -1).
+# - Remove the colon from [H]H:MM to gain numeric comparability.
+# - Sort/merge the arrival/departure lists by time and event.  Presuming
+#   arrivals to occur before simultaneous departures and thus forbidding
+#   the usage of the same platform for such.
+# - Count the current and maximum number of present trains at each
+#   event.
+# - The first element of the reduce result is the maximum number of
+#   simultaneously present trains and therefore the requested minimum
+#   number of required platforms.
+sub platforms ($arrivals, $departures) {
+    (reduce {[$a->[($a->[1] += $b->[1]) > $a->[0]], $a->[1]]}
+        ['-inf', 0], sort {$a->[0] <=> $b->[0] || $b->[1] <=> $a->[1]}
+        map {$_->[0] =~ tr/://d; $_}
+        map([$_, 1], @$arrivals), map([$_, -1], @$departures))->[0];
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+        is platforms([qw(11:20 14:30)], [qw(11:50 15:00)]), 1, 'example 1';
+        is platforms([qw(10:20 11:00 11:10 12:20 16:20 19:00)],
+            [qw(10:30 13:20 12:40 12:50 20:20 21:20)]), 3, 'example 2';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+        is platforms([qw(9:30 10:00)], [qw(10:15 10:30)]), 2, 'one digit hour';
+        is platforms([qw(09:30 10:00)], [qw(10:15 10:30)]), 2, 'leading zero';
+        is platforms([qw(1:00 1:10)], [qw(1:10 1:20)]), 2,
+            'no simultaneous arrival and departure at the same platform';
+	}
+
+    done_testing;
+    exit;
+}
-- 
cgit