Did you bench it. It looks that hashset is not required or is slower that this solution. Probable because L3 cache

Better constant time factor or caching maybe?

Elegant solve. Thanks for the commented version -- most insightful.

Still a pure function because in order for it to be impure , it would have to access variables OUTSIDE of the function call...this function would always output the exact same thing if given the same input because there is no outside state effecting what happens inside the function...

not really, what if you have a program of O(1)?

(a.pop()|0) + (b.pop()|0) works (same effect as doing ~~)

Although you can compress a range, the enumeration is faster.

Run it through the naive implementation, get back to me when that has come up with an answer ..

I like your solution, just use strings.Builder instead concatenaning strings

The kata is OK, the test is not extreme

Did that Ruby undef require solve Blind's issue? I see invalid solutions that use it; it certainly seems so ( thanks! ).

Is that a Python problem, or just plain a CW problem? The DP solutions I see should be able to run within a reasonabe amount of time; it really doesn't look like the algorithms are that bad.

I tried to create a Python translation, but a Ruby 1.2s solution, in Python, with a lot less tests, runs in 10s. terrible.

Maybe it'll get shot down as a duplicate

it would, since most of the solutions to yours are actually solutions to a "ludicrous" one