Solution to task 2

1 files changed, 87 insertions, 0 deletions

diff --git a/challenge-088/jo-37/perl/ch-2.pl b/challenge-088/jo-37/perl/ch-2.pl
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+++ b/challenge-088/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl
+
+use 5.012;
+use PDL;
+use Test2::V0 '!float';
+use experimental 'postderef';
+
+{
+	# Instructions for the unrolling engine:
+	# - edge (as slice arg)
+	# - remaining matrix (as slice arg)
+	# - affected dimension (row or column)
+	# by direction.
+	my @instr = (
+		['X,(0)', 'X,1:-1', 1],		# first row, east
+		['(-1),X', '0:-2,X', 0],	# last column, south
+		['-1:0,(-1)', 'X,0:-2', 1],	# last row, west
+		['(0),-1:0', '1:-1,X', 0]);	# first column, north
+
+	# Unroll given matrix, i.e. return the elements as a 1-d list in
+	# spiral form.
+	sub unroll {
+		# Input matrix, starting direction and result.
+		my ($m, $dir, $unrolled) = (long(shift), 0, PDL->null);
+
+		say $m;
+		die "not a matrix" unless $m->ndims == 2;
+
+		while (1) {
+			# Get the instructions.
+			my ($edge, $remaining, $dim) = $instr[$dir]->@*;
+
+			# Append current edge to the result.
+			$unrolled = $unrolled->append($m->slice($edge));
+
+			# Stop if the current edge was the last remaining dimension.
+			last if $m->dim($dim) == 1;
+
+			# Take the remaining matrix.
+			$m = $m->slice($remaining);
+
+			# Switch direction.
+			$dir = ($dir + 1) % 4;
+		}
+
+		say $unrolled;
+		$unrolled->unpdl;
+	}
+}
+
+# Test cases by ending direction and number of trailing elements.
+is unroll(sequence(long, 3, 3) + 1),
+	[1, 2, 3, 6, 9, 8, 7, 4, 5], 'east-1 (Example 1)';
+
+is unroll(sequence(long, 4, 3) + 1),
+	[1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7], 'east-2';
+
+is unroll(sequence(long, 3, 4) + 1),
+	[1, 2, 3, 6, 9, 12, 11, 10, 7, 4, 5, 8], 'south-1';
+
+is unroll(sequence(long, 3, 5) + 1),
+	[1, 2, 3, 6, 9, 12, 15, 14, 13, 10, 7, 4, 5, 8, 11], 'south-2';
+
+is unroll(sequence(long, 4, 4) + 1),
+	[1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, 5, 6, 7, 11, 10],
+	'west-1 (Example 2)';
+
+is unroll(sequence(long, 5, 4) + 1),
+	[1, 2, 3, 4, 5, 10, 15, 20, 19, 18, 17, 16, 11, 6, 7, 8, 9, 14, 13, 12],
+	'west-2';
+
+is unroll(sequence(long, 4, 5) + 1),
+	[1, 2, 3, 4, 8, 12, 16, 20, 19, 18, 17, 13, 9, 5, 6, 7, 11, 15, 14, 10],
+	'north-1';
+
+is unroll(sequence(long, 4, 6) + 1),
+	[1, 2, 3, 4, 8, 12, 16, 20, 24, 23, 22, 21, 17, 13, 9,
+		5, 6, 7, 11, 15, 19, 18, 14, 10], 'north-2';
+
+# other tests
+is unroll([[1, 2], [3, 4]]), [1, 2, 4, 3], 'non-piddle arg';
+is unroll([[1, 2]]), [1, 2], 'single row';
+is unroll([[1],[2]]), [1, 2], 'single column';
+is unroll([[1]]), [1], 'single element';
+like dies {unroll [1]}, qr/^not a matrix/, 'not a matrix';
+
+done_testing;