For O(n) only way is convert b to hash.

Why isn't the time complexity O(n^2)? For each element in a, you need to scan the whole content of b. (Unless Ruby does something better under the hood).

The time complexity is O(n).
@daniel: Time complexity != execution time.

i am interested as well, but not enough to run some quick benchmarks myself^^

#clamp – niiiice!

Everything's fine with the kata.

Interesting what is the Time complexity for this solution?

Since ruby 2.4 it's built-in, see my fork

same here!

I have similar situation with javascript. My own test cases all pass, but I get pageIndex returned incorrect value error during final submission. I wish there were more details to help me understand whether my code is actually broken or there is an issue in test cases..

Interesting method/name: #clamp.

5 kyu, really? This is a trivial kata.

This is a very nice kata. Though my solution is shit :)

Under Ruby, my 10s of tests all pass. Then, when I submit, I get this:

page_index returned incorrect value when provided a item_index argument that was out of range

The tests provided in the discription pass too.