Seriously, why would one want to do that, other than not being in an Oracle environment? Don't tell me it's an exam/homework question.

You can, but not in a single statement. Here's what Tom Kyte learns us at his site (asktom.oracle.com):
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in a single statement -- no, relational algebra doesn't permit it. Entirely
duplicate records (where all columns are the same) make this not possible.

using rownum -- no, you cannot use rownum either.

Using rowid, yes, you can use rowid.

Using procedural code, yes, you can use procedural code.

Using more then one statement, yes, I can do this in 3 statements:

insert dups into temp table
delete dups from orig table
put de-duped data back into orig table from temp table

But I came across some solutions, but they're all Oracle specific (using analytic functions). If your interested search the site.