So, you are stepping through two arrays using foreach $a and foreach $b, and in the inner loop you need the indexes for $a ($acount) and $b ($acount).

You are incrementing $acount and $bcount in the right place -- but you need to set $bcount to zero just before the foreach $b. I suggest that this accounts for your immediate problem.

Other's have pointed out that delete on arrays doesn't actually remove an array element, and if it did who knows whether foreach would cope.

From a style perspective I suggest that calling these indexes $acount obscures their purpose -- which is probably why the problem was hard to see. I would have called them $ia and $ib. Probably best to stick the initialisation of the index hard up against the related foreach.

Also, from a style perspective I wonder whether:

  my $ia = 0 ;
  foreach my $a (@afoo) {

    ... acres of stuff ...

    $ia++ ;
  } ;
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is as clear as:

  for my $ia (0..$#afoo) {
    my $a = $afoo[$ia] ;


  } ;
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because in the second case the loop control is all at the top of the loop. Mind you, the two are not equivalent, because of the quantum entanglement between $a and the array element in the first ! Perhaps better is:

  my $ia = -1 ;
  foreach my $a (@afoo) {
    $ia++ ;

    ......

  } ;
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although I cannot help feeling that setting $ia to -1 is ugly :-(