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

It is impossible to solve this problem without making comparisons. Some modern languages do have set difference and other aggregate operators, but they work by internally making comparisons. If the total array size is odd (not the case here) then it does work to xor the elements together. I suppose the question of whether the ALU's xor op should be considered a comparison is debatable.

And without specifying a language, you can't refer to a library, so the only possible solution is a comparison-based pseudo-code exposition.

So here you go:

a <- first element
a_count = 1
b_count = 0
loop over remaining elements
   if element != a
     b <- element
     ++b_count
   else
     ++a_count
   if found_result
      break loop
end loop

found_result
   if a_count > 1 and b_count > 0
     the unique one is b
     return true
   if b_count > 1 and a_count > 0 # a_acount actually always > 0
     the unique one is a
     return true
   return false