#!/usr/bin/perl
#
# Matrix Spiral
#
use strict;
use warnings;

#
# Size of input matrix in columns and rows
#
my $cols = 7;
my $rows = 3;

#
# Decrement rows & columns because we're using them as array indices
# (i.e. counting from 0 not 1)
#
$cols--;
$rows--;


#
# Populate a list of elements to feed the matrix from
#
my @elements;

while (<DATA>) {

    #
    # Display data to screen so we can compare results to it
    #
    print;

    push @elements, (split(' ', $_));

}

#
# Keep the size of elements for after we've shifted it empty
#
my $count = @elements;

#
# Populate a matrix of the elements
# which pacman can then walk around & eat pill by pill...
#
my @matrix;

for my $row (0 .. $rows ) {

    for my $col (0 .. $cols ) {

        $matrix[$col][$row] = shift(@elements);

    }

}

my @output;

my $x = 0; # X position in matrix
my $y = 0; # Y position in matrix

my $v = 0; # Vertical direction
my $h = 1; # Horizontal direction

my $row_s = 0;     # Current Row start
my $row_e = $rows; # Current Row end
my $col_s = 0;     # Current Column start
my $col_e = $cols; # Current Column end

for my $place ( 0 .. $count-1 ) {

    #
    # Show X and Y coordinate in bounds "min<coord<max"
    # and the value at that coordinate in [ ] so we can see it work
    #
    print "$place x[$col_s<$x<$col_e] y[$row_s<$y<$row_e]",
        " [$matrix[$x][$y]]\n";

    #
    # Push the element at that matrix coordinate into the output list
    #
    $output[$place] = $matrix[$x][$y];

    if ( $h == 1 && $v == 0 && $x == $col_e && $y == $row_s ) {

        print "> reached last col. go v\n";

        $h = 0; # Stop horizontal movement (was right)
        $v = 1; # Go down

        # Finished highest remaining row
        # so remove it from matrix bounds
        $row_s++;

    }
    elsif ( $h == 0 && $v == 1 && $x == $col_e && $y == $row_e ) {

        print "v reached last row. go <\n";

        $h = -1; # Go left
        $v = 0; # Stop vertical movement (was down)

        # Finished rightmost remaining column
        # so remove it from matrix bounds
        $col_e--;

    }
    elsif ( $h == -1 && $v == 0 && $x == $col_s && $y == $row_e ) {

        print "< reached first col. go ^\n";

        $h = 0; # Stop horizontal movement (was left)
        $v = -1; # Go up

        # Finished lowest remaining row
        # so remove it from matrix bounds
        $row_e--;

    }
    elsif ( $h == 0 && $v == -1 && $x == $col_s && $y == $row_s ) {

        print "^ reached first row. go >\n";

        $h = 1; # Go right
        $v = 0; # Stop vertical movement (was up)

        # Finished leftmost remaining column
        # so remove it from matrix bounds
        $col_s++;

    }

    #
    # Increment (or decrement) matrix position pointer
    #
    $x += $h;
    $y += $v;

}

print join($/, @output), $/;

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