Distinguishing extra element from two arrays?

Question

One of my friend was asked this question in an interview -

• You have given two integer arrays each of size 10.
• Both contains 9 equal elements (say 1 t

Answer 1

Make sets A, B of the arrays a,b respectively. A \ B gives you the additional integer in A. B \ A gives you the additional integer in B.

If either one of these operations returns an empty set, then the additional integer is in the array twice. You find this out when constructing the set: adding a duplicate integer to the set does not increase the set's size.