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

my @matrix = ( [ 1,  2,  3,  4],
               [ 5,  6,  7,  8],
               [ 9, 10, 11, 12],
               [13, 14,  3, 16],
               [ 2, 18, 19, 20],
             );

sub nearby {
    my @input = @_;
    my %numbers;
    undef @numbers{@input};

    for my $y (0 .. $#matrix) {
        for my $x (0 .. $#{ $matrix[$y] }) {
            next unless exists $numbers{ $matrix[$y][$x] };

            my @next = ([$x, $y]);
            my %visited;
            while (@next) {
                my ($r, $s) = @{ shift @next };
                undef $visited{ $matrix[$s][$r] }{"$r $s"};
                return 1 if keys %visited == keys %numbers;

                push @next, grep $_->[0] >= 0 && $_->[1] >= 0
                            && $_->[0] <= $#{ $matrix[$s] } && $_->[1] <= $#matrix
                            && exists $numbers{ $matrix[ $_->[1] ][ $_->[0] ] }
                            && ! exists $visited{ $matrix[ $_->[1] ][ $_->[0] ] }{"@$_"},
                        [$r - 1, $s - 1],
                        [$r,     $s - 1],
                        [$r + 1, $s - 1],
                        [$r + 1, $s    ],
                        [$r + 1, $s + 1],
                        [$r,     $s + 1],
                        [$r - 1, $s + 1],
                        [$r - 1, $s    ];
                # warn map "<@$_>", @next;
            }
        }
    }
    return
}

use Test::More;

ok(nearby(2, 7, 12, 16));
ok(nearby(2, 4, 7, 12));
ok(! nearby(1, 6, 8, 12));
ok(! nearby(1, 5, 14, 15));

# Unspecified?
ok(nearby(2, 13, 9, 5, 7));
ok(! nearby(2, 13, 7));
ok(nearby(6, 3, 8, 12, 18));

@matrix = ( [ 1,  1,  1,  1, 2],
            [ 1,  0,  0,  0, 0],
            [ 1,  0,  1,  1, 3],
            [ 1,  0,  1,  0, 0],
            [ 1,  0,  1,  1, 1],
            [ 1,  0,  0,  0, 1],
            [ 1,  1,  1,  1, 1],
          );
ok(nearby(1, 2, 3));

done_testing();