[mike_kamau]

Could you please add a description to your solution?

[soegaard]

Here is a Racket (/Scheme) version of the JavaScript solution with a thorough explanation.

http://pasterack.org/pastes/80529

Note that this solution is using a standard imperative style, with a loop over that narrows down the location of the sought of element in two subvectors of a and b.

[cousin_it]

Wow! Yes, this is all exactly right.