This is iterating the list twice so it's not the most efficient solution if large lists were involved.

the order of the solution does not change the factors. Great.

"in" is faster with Set or dict. But I like the use of format

exactly what i did

I like this solution and I was going for something similar, but it fails if the "unique" string is alphabetically in between two "non-unique" strings. For example the following test fails:

test.assert_equals(find_uniq([ 'abz', 'azb', 'baz', 'foo', 'bza', 'zab', 'zba' ]), 'foo')

Am I missing something here?

Dunno but I did it lol

Unexpected solution. I was thinking about hash tables

nice and simple, good idea

Same idea, but executed a bit different.

nice, never knew this concept.

And what if the area code was, say, 4 digits long?