comment on

"AND" is not really possible in regexes. You have to use advanced tricks such as positive lookaheads.

/^(?=.*[A-Za-z])(?=.*[0-9])[A-Za-z0-9]{3,10}\z/
[download]

Of course, you could possibly use multiple regexs for increased readability.

/^[A-Za-z0-9]{3,10}\z/ && /[A-Za-z]/ && /[0-9]/
[download]

Update: For fun,

Eliminates one lookahead:

/^(?=[A-Za-z0-9]{3,10}\z).*(?:[0-9][A-Za-z]|[A-Za-z][0-9])/
[download]

Eliminates both lookahead:

/(?>(?:[0-9][A-Za-z]|[A-Za-z][0-9]).*\z)(?(?{pos()<3||pos()>10})(?!))/
[download]

All tested.

Update: Benchmarked. (Benchmarking Code, a prime example of a good Benchmark if you ask me.)

----------------------------------------
Short (arg: 2j)

            Rate ikegami4 ikegami3 ikegami2 ikegami1
ikegami4  573/ms       --     -60%     -76%     -77%
ikegami3 1428/ms     149%       --     -40%     -44%
ikegami2 2392/ms     318%      68%       --      -5%
ikegami1 2529/ms     342%      77%       6%       --

----------------------------------------
Fine (arg: n4a1z9)

           Rate ikegami4 ikegami2 ikegami1 ikegami3
ikegami4 638/ms       --     -11%     -18%     -20%
ikegami2 715/ms      12%       --      -8%     -10%
ikegami1 776/ms      22%       9%       --      -2%
ikegami3 794/ms      24%      11%       2%       --

----------------------------------------
Just Letters (arg: nhfdmzaa)

           Rate ikegami4 ikegami3 ikegami2 ikegami1
ikegami4 397/ms       --     -16%     -44%     -45%
ikegami3 471/ms      19%       --     -34%     -35%
ikegami2 714/ms      80%      52%       --      -2%
ikegami1 728/ms      83%      55%       2%       --

----------------------------------------
Long (arg: qq3m3aaaazz3)

            Rate ikegami4 ikegami1 ikegami3 ikegami2
ikegami4  157/ms       --     -79%     -88%     -89%
ikegami1  746/ms     376%       --     -45%     -45%
ikegami3 1351/ms     762%      81%       --      -1%
ikegami2 1365/ms     770%      83%       1%       --
[download]

My first choice based solely on benchmarks would be ikegami2 (the three regexps).
My first choice based solely on benchmarks would be ikegami1 (straightforward lookahead).

In reply to Re: A hard RegEx problem. by ikegami
in thread A hard RegEx problem. by pysome

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