What you have is essentially a hash. array_b is your keys, array_a is your values:

my %h;
@h{@array_b} = @array_a;
# Now you can sort however you want, and they're linked:
for (sort {$a <=> $b} keys %h) {
  print "$_: $h{$_}\n";
}
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If array_b starts at zero and doesn't skip values, you can use an array similarly:

my @sorted_values;
@sorted_values[@array_b] = @array_a; # magically sorted!
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If it skips some values (but doesn't range into absurdly high numbers) and/or doesn't start at zero, you can grep out the undefs (assuming you don't have valid undef values):

# same as above, then
@sorted_values = grep defined, @sorted_values;
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