Here's one I came up against on the weekend.

I have an object representing part of a space of N dimensions. This object has neighbours (e.g. if N is 1, it has 8 neighbours:

NNN
N*N
NNN

Now I need to get the co-ordinates of all my neighbours, assuming I have my own co-ordinates.

This seems to require setting up N nested for loops, each of them going for(-1,0,1){}. I couldn't think of an elegant way to do this, perhaps because I don't have a formal CS background.

In the end I produced a hack. NB, to understand this, you must realise that I only wanted my neighbours nearer the origin. Otherwise the hack would not have worked.

my $possibilities = 2 ** $N; # $N is number of dimensions
# @mypos is my coordinates.
for (1 .. $possibilities) { # using 0 would return my own position
 my $binary = sprintf '%b', $_;
 my $pad= '0' x ($N - length $binary);
 $binary = $pad.$binary;
 my @shift = split //, $binary;
 my @pos = map {$mypos[$_] - $shift[$_]} 0 .. $#mypos;
 push @neighbours, \@pos;
}

[download]

This is neat but fundamentally evil, and I wondered if someone had a better solution. (Recursion?)

dave hj~

In reply to getting my neighbours in an N-dimensional space by dash2

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