push @{$_ & 1 ? \ @odd : \ @even }, $_ for @nums;

##</code><code>##

@nums = 1..20;
/.*(?=.)([13579]$)?(?(1)(?{${"\@nums::${_}::"}++})|(?{${"\@nums::${_}::"}--}))/ for @nums;
printf "%d %s\n", $_, ${"\@nums::$_"} > 0 ? odd : even for keys %{"\@nums::"};