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Re: breaking an array into nearly equal parts

by revdiablo (Prior)
on Dec 14, 2005 at 02:06 UTC ( #516499=note: print w/replies, xml ) Need Help??


in reply to breaking an array into nearly equal parts

Did you notice a pattern in the table you pasted? It looks like it contains all the information you need. It's basically like this:

If $x%3 is 0, the arrays should all be of size $x/3. If $x%3 is not 0, there should be $x-($x%3) arrays of size $x/3 and $x%3 of size $x/3+1.

I'm not positive this will continue to hold true, but it looks good from what you've shown. There may be a simpler algorithm too, so I would be happy to see other replies. :-)

Replies are listed 'Best First'.
Re^2: breaking an array into nearly equal parts
by spiritway (Vicar) on Dec 14, 2005 at 05:40 UTC

    You're right - and the pattern holds true. A positive integer can either be exactly divisible by three, have a remainder of 1, or a remainder of 2. Your idea is probably one of the simplest.

      It is quite simple. Here's an implementation. The apportion figures out chunk sizes; multi_slice returns slices of those sizes. The for block runs a few examples.
      sub apportion { my ($elements, $pieces) = @_; my $small_chunk = int $elements / $pieces; my $oversized_count = $elements % $pieces; ((1 + $small_chunk) x ($oversized_count), ($small_chunk) x ($pieces +- $oversized_count)); } sub multi_slice { my ($aref, @chunk_sizes) = @_; my $hi_i = -1; map { my $lo_i = $hi_i + 1; $hi_i += $_; [@$aref[$lo_i..$hi_i]] } @chunk_sizes; } for my $try ([16,3], [17,4], [19,3]) { print "$try->[0] elements into $try->[1] pieces:\n"; print "Sizes: ", join(', ', apportion(@$try)), "\n"; print "@$_\n" for multi_slice([1..$try->[0]], apportion(@$try)); }

      Caution: Contents may have been coded under pressure.

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