Solution to task 2

1 files changed, 85 insertions, 0 deletions

diff --git a/challenge-199/jo-37/perl/ch-2.pl b/challenge-199/jo-37/perl/ch-2.pl
new file mode 100755
index 0000000000..292be9b25e
--- /dev/null
+++ b/challenge-199/jo-37/perl/ch-2.pl
@@ -0,0 +1,85 @@
+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0 '!float';
+use PDL;
+use experimental 'signatures';
+
+our ($tests, $examples, $verbose);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS if @ARGV < 5;
+usage: $0 [-examples] [-tests]  [X Y Z N1 N2...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+X Y Z
+    limits for absolute pair differences
+
+N1 N2...
+    list of values
+EOS
+
+
+### Input and Output
+
+say count_good_3(@ARGV);
+
+
+### Implementation
+
+# This task may be regarded as a variant of challenge 196/1 and is very
+# similar to this week's task 1.  The first transformation step is from
+# index i to index j > i having an absolute value difference not
+# exceeding X.  The second step goes from index j to index k > j having
+# an absolute value difference not exceeding Y. The third step goes from
+# index k to index l < k having an absolute value difference not
+# exceeding Z, where i shall be equal to l.  The possible starting
+# indices then are given by the nonzero elements in the diagonal of the
+# resulting product matrix.  Actually, the diagonal has the number of
+# solutions for every starting index and thus the sum over the diagonal
+# is the requested number of good triplets.
+# See
+# https://github.com/manwar/perlweeklychallenge-club/blob/master/challenge-196/jo-37/perl/ch-1.pl
+# for details.
+sub count_good_3 ($x, $y, $z, @l) {
+    # Need a "double" piddle capable of holding 'inf' values.
+	my $l = pdl @l;
+    # Create the matrix of absolute pair differences.
+    my $adt = ($l - $l->dummy(0))->abs;
+    # Combining the difference matrix and the index transition matrix by
+    # invalidating the upper right triangle values (including the
+    # diagonal) utilizing symmetry.
+    $adt->where($l->sequence >= $l->sequence->dummy(0)) .= 'inf';
+        
+    # Build transformation matrices and chain them.  Then sum over the
+    # diagonal.
+    (($adt <= $z)->xchg(0, 1) x ($adt <= $y) x ($adt <= $x))
+        ->diagonal(0, 1)->sum;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is count_good_3(qw(7 2 3 3 0 1 1 9 7)), 4, 'example 1';
+        is count_good_3(qw(0 0 1 1 1 2 2 3)), 0, 'example 2';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+        
+        is count_good_3(1, 1, 2, 0, 3, 1, 5, 2, 5), 1, 'single triplet';
+	}
+
+    done_testing;
+    exit;
+}