The first approach isn't O(N) because of the lookup in the hash. Update: for the impatients that don't want to look further in the subthread, this comment ended up to be incorrect.

Flavio
perl -ple'$_=reverse' <<<ti.xittelop@oivalf

Don't fool yourself.

In reply to Re^2: Combining arrays with grep/unless? by polettix
in thread Combining arrays with grep/unless? by mdunnbass

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