perl -MTime::HiRes=time 
-E"$t=time;my @a; $a[$_]=1 for 1..1e6; printf qq[%f\n], time()-$t"
0.220181

perl -MTime::HiRes=time 
-E"$t=time;my %h; $h{$_}=1 for 1..1e6; printf qq[%f\n], time()-$t"
1.805000