$ perl 939870.pl 1000
Building arrays of 1000 with unique 4-char keys... done.
Arrays have 1000 items each. Benchmarking...
                    Rate  arrays plus regex     using a hash
arrays plus regex   2.70/s             --            -100%
using a hash    1000000000000000/s 37000000000000000%  --              

$ perl 939870.pl 5000
Building arrays of 5000 with unique 4-char keys... done.
Arrays have 5000 items each. Benchmarking...
                    s/iter arrays plus regex      using a hash
arrays plus regex     9.40                --             -100%
using a hash      1.00e-02            93900%                --

$ perl 939870.pl 10000
Building arrays of 10000 with unique 4-char keys... done.
Arrays have 10000 items each. Benchmarking...
                    s/iter arrays plus regex      using a hash
arrays plus regex     46.3                --             -100%
using a hash      3.00e-02           154267%                --

$ perl 939870.pl 100000
Building arrays of 100000 with unique 4-char keys... done.
Arrays have 100000 items each. Benchmarking...
                  s/iter arrays plus regex      using a hash
arrays plus regex   4110                --             -100%
using a hash       0.330          1245345%                --