I don't remember if it was quicker, but there also is the non-looped version: 
undef %saw;
@saw{@in} = (1) x @in;
@out = keys %saw;

[download]
I haven't benchmarked it, but I've frequently heard it asserted that even faster is 
undef %saw;
@saw{@in} = ();
@out = keys %saw;

[download]
That is, using undef as your values (so you don't need the increment or to create the list of ones).

In reply to Re^2: What does !$saw{$_}++ means by Eimi Metamorphoumai
in thread What does !$saw{$_}++ means by nwkcmk

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