I agree with antong01. This problem is best solved in O(n) by not sorting either array, but instead making use of a dictionary. Most of the solutions submitted either use sorting which results in O(n log n) or searching through an array, which results in O(n^2) overall. While simple and concise to write, they don't scale as well.

While this is a simple solution, it has complexity of O(n log n); For big arrays it could be suboptimal if the first first element of a didn't have a match (no early return) or if b was an empty array

Use spoiler flag please.

I didn't think there would be, but that's good to know. Cool!

I did some benchmarking, did each 10,000,000 times several times, can't find any differences outside of the margin of error.

Thank you very much for your help. Now, I can apply that new trick to my future problems. Have a nice day. :)

try this: http://ruby-doc.org/core-2.2.0/String.html#method-i-5B-5D

Could somebody tell me where could I the explaination for this one in the Ruby API? Thanks in advance, and have a nice day.