Solution to task 2

1 files changed, 66 insertions, 0 deletions

diff --git a/challenge-236/jo-37/perl/ch-2.pl b/challenge-236/jo-37/perl/ch-2.pl
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+++ b/challenge-236/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.25;
+use Test2::V0;
+use Math::Permutation;
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [N...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+N...
+    zero-based permutation of any size in one-line notation
+
+EOS
+
+
+### Input and Output
+
+say cycles(@ARGV);
+
+
+### Implementation
+
+# As the given numbers shall be unique and at the same time be indices
+# into an array of the same size, they actually represent a zero-based
+# permutation in one-line notation.  This task asks for the number of
+# cycles.  Transforming the numbers into a one-based one-line notation,
+# creating a permutation thereof, converting to cycles and counting
+# these with the help of CY's Math::Permutation module.
+
+sub cycles {
+    scalar Math::Permutation->wrepr([map $_ + 1, @_])->cyc->@*;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+        
+        is cycles(4,6,3,8,15,0,13,18,7,16,14,19,17,5,11,1,12,2,9,10),
+            3, 'example 1';
+        is cycles(0,1,13,7,6,8,10,11,2,14,16,4,12,9,17,5,3,18,15,19),
+            6, 'example 2';
+        is cycles(9,8,3,11,5,7,13,19,12,4,14,10,18,2,16,1,0,15,6,17),
+            1, 'example 3';
+
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+	}
+
+    done_testing;
+    exit;
+}