From 784f3a7dbf8ce42f6f4f147fbcb821365772cd83 Mon Sep 17 00:00:00 2001
From: Jörg Sommrey <28217714+jo-37@users.noreply.github.com>
Date: Tue, 23 May 2023 10:58:57 +0200
Subject: Solution to task 2

---
 challenge-218/jo-37/perl/ch-2.pl | 89 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)
 create mode 100755 challenge-218/jo-37/perl/ch-2.pl

diff --git a/challenge-218/jo-37/perl/ch-2.pl b/challenge-218/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..6c67fa4ac0
--- /dev/null
+++ b/challenge-218/jo-37/perl/ch-2.pl
@@ -0,0 +1,89 @@
+#!/usr/bin/perl -s
+
+use v5.24;
+use Test2::V0 '!float';
+use PDL;
+use PDL::NiceSlice;
+use Math::Prime::Util 'fromdigits';
+use experimental 'signatures';
+
+our ($tests, $examples, $verbose);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [-verbose] [--] [...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+-verbose
+    enable trace output
+
+M
+    matrix from zeroes and ones in any form accepted by the PDL string
+    constructor, e.g.
+    "[ [0,0,1,1], [1,0,1,0], [1,1,0,0], ]"
+
+EOS
+
+
+### Input and Output
+
+say matrix_score(byte "@ARGV");
+
+
+### Implementation
+
+# The matrix is maximal w.r.t. row toggles if the first column is
+# all-ones.  Any toggled row would decrease the overall sum.
+# The matrix is maximal w.r.t. column toggles, if all columns have at
+# least as many ones as zeroes.  Toggling a column having an equal
+# number of zeroes and ones would not change the overall sum whereas the
+# overall sum would decrease otherwise.
+
+sub matrix_score ($b) {
+    say "inititial:", $b if $verbose;
+    
+    # Toggle all rows having a zero in the first column.
+    $b ^= !$b(0);
+    say "intermediate:", $b if $verbose;
+    
+    # Toggle all columns having less ones than zeroes.
+    $b ^= $b->xchg(0, 1)->sumover < $b->dim(1) / 2;
+    say "final:", $b if $verbose;
+
+    # Fromdigits accepts digits of any size, thus there is no need to
+    # calculate the individual numbers.
+    fromdigits $b->xchg(0, 1)->sumover->unpdl, 2;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    local $verbose;
+
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is matrix_score(byte [0,0,1,1], [1,0,1,0], [1,1,0,0]), 39, 'example 1';
+        is matrix_score(byte [[0]]), 1, 'example 2';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is matrix_score(byte [1, 1, 0, 0, 0, 1], [0, 0, 0, 1, 1, 1],
+            [1, 0, 1, 1, 0, 0], [0, 1, 1, 0, 0, 1], [1, 0, 0, 0, 1, 1]),
+            253, 'toggle all but first columns';
+            # 32 * 5 + (16 + 8 + 4 + 2 + 1) * 3
+
+	}
+
+    done_testing;
+    exit;
+}
-- 
cgit