## Advent Calendar - December 15, 2021

Wednesday, Dec 15, 2021| Tags: Perl, Python

### | Day 14 | Day 15 | Day 16 |

The gift is presented by Lubos Kolouch. Today he is talking about his solution to “The Weekly Challenge - 088”. This is re-produced for Advent Calendar 2021 from the original post by `Lubos Kolouch`.

You are given `m x n` matrix of positive integers.

Write a script to print spiral matrix as list.

If you want to think like a robot traversing enemy area, you have to become a `robot`.

I liked this exercise as there will be certainly similar in the coming `Advent Of Code`!

I decided to be in the position of a robot crawling the array, going in a direction as far as I can and then change the direction at the end. At the same time keep track of the fields I have seen.

## From the code:

### Perl:

``````my \$x_max = scalar @\$in_arr;
my \$y_max = scalar @{\$in_arr->[0]};

my @pos = (0, 0);
my \$direction = ">";

my %seen_cells;
my @out_arr;
``````

### Python:

``````x_max = len(in_arr)
y_max = len(in_arr[0])

pos = [0,0]
direction = ">"

seen_cells = {}
out_arr = []
``````

### Perl:

``````while (1) {

return \@out_arr if scalar @out_arr == \$x_max * \$y_max;

push @out_arr, \$in_arr->[\$pos[0]][\$pos[1]] unless \$seen_cells{\$pos[0]}{\$pos[1]};
\$seen_cells{\$pos[0]}{\$pos[1]} = 1;
``````

### Python:

``````while 1:

if len(out_arr) == x_max * y_max:
return out_arr

if seen_cells.get((pos[0], pos[1]), 0 ) == 0:
out_arr.append(in_arr[pos[0]][pos[1]])

seen_cells[(pos[0], pos[1])] = 1
``````

### Perl:

``````# can move in the direction we are walking?
if (\$direction eq ">") {
if ((\$pos[1] + 1 < \$x_max) and not (\$seen_cells{\$pos[0]}{\$pos[1]+1})) {
\$pos[1]++;
} else {
\$direction = "v";
}
}
``````

### Python:

``````if direction == ">":
if (pos[1] + 1 < x_max) and not (seen_cells.get( (pos[0], pos[1]+1), 0) ):
pos[1] += 1
else:
direction = "v"
``````

## Complete Code

### Perl:

``````#!/usr/bin/perl
#===============================================================================
#
#         FILE: ch-2.pl
#
#        USAGE: ./ch-2.pl
#
#  DESCRIPTION: https://perlweeklychallenge.org/blog/perl-weekly-challenge-088/
#                  Spiral Matrix
#
#       AUTHOR: Lubos Kolouch
#      VERSION: 1.0
#      CREATED: 11/28/2020 01:02:17 PM
#===============================================================================

use strict;
use warnings;

sub get_spiral{
my \$in_arr = shift;

my \$x_max = scalar @\$in_arr;
my \$y_max = scalar @{\$in_arr->[0]};

my @pos = (0, 0);
my \$direction = ">";

my %seen_cells;
my @out_arr;

while (1) {

return \@out_arr if scalar @out_arr == \$x_max * \$y_max;

push @out_arr, \$in_arr->[\$pos[0]][\$pos[1]] unless \$seen_cells{\$pos[0]}{\$pos[1]};
\$seen_cells{\$pos[0]}{\$pos[1]} = 1;

# can move in the direction we are walking?
if (\$direction eq ">") {
if ((\$pos[1] + 1 < \$x_max) and not (\$seen_cells{\$pos[0]}{\$pos[1]+1})) {
\$pos[1]++;
} else {
\$direction = "v";
}
}

elsif (\$direction eq "v") {
if ((\$pos[0] + 1 < \$y_max) and not (\$seen_cells{\$pos[0]+1}{\$pos[1]})) {
\$pos[0]++;
} else {
\$direction = "<";
}
}

elsif (\$direction eq "<") {
if ((\$pos[0] - 1 >= 0) and not (\$seen_cells{\$pos[0]-1}{\$pos[1]})) {
\$pos[0]--;
next;
} else {
\$direction = "^";
}
}

elsif (\$direction eq "^") {
if ((\$pos[1] - 1 >= 0) and not (\$seen_cells{\$pos[0]}{\$pos[1]-1})) {
\$pos[1]--;
next;
} else {
\$direction = ">";
}
}

}

}

use Test::More;

is_deeply(get_spiral([[1, 2, 3], [4, 5, 6], [7, 8, 9]]), [1, 2, 3, 6, 9, 8, 7, 4, 5]);
is_deeply(get_spiral([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]), [1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, 5, 6, 7, 11, 10 ]);

done_testing();
``````

### Python:

``````#!/bin/env python
#===============================================================================
#
#         FILE: ch-2.py
#
#        USAGE: ./ch-2.py
#
#  DESCRIPTION: https://perlweeklychallenge.org/blog/perl-weekly-challenge-088/
#                  Spiral Matrix
#
#       AUTHOR: Lubos Kolouch
#      VERSION: 1.0
#      CREATED: 11/28/2020 01:02:17 PM
#===============================================================================

def get_spiral(in_arr):

x_max = len(in_arr)
y_max = len(in_arr[0])

pos = [0,0]
direction = ">"

seen_cells = {}
out_arr = []

while 1:

if len(out_arr) == x_max * y_max:
return out_arr

if seen_cells.get((pos[0], pos[1]), 0 ) == 0:
out_arr.append(in_arr[pos[0]][pos[1]])

seen_cells[(pos[0], pos[1])] = 1

# can move in the direction we are walking?
if direction == ">":
if (pos[1] + 1 < x_max) and not (seen_cells.get( (pos[0], pos[1]+1), 0) ):
pos[1] += 1
else:
direction = "v"

elif direction == "v":
if (pos[0] + 1 < y_max) and not (seen_cells.get( (pos[0]+1, pos[1]), 0) ):
pos[0] += 1
else:
direction = "<"

elif direction == "<":
if (pos[0] - 1 >= 0) and not (seen_cells.get( (pos[0]-1, pos[1]), 0) ):
pos[0] -= 1
else:
direction = "^"

elif direction == "^":
if (pos[1] - 1 >= 0) and not (seen_cells.get( (pos[0], pos[1]-1), 0) ):
pos[1] -= 1
else:
direction = ">"

assert get_spiral([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == [1, 2, 3, 6, 9, 8, 7, 4, 5]
assert get_spiral([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]]) == [1, 2, 3, 4, 8, 12, 16, 15, 14, 13, 9, 5, 6, 7, 11, 10 ]
``````

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