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

Put each element of the first array into a hash. For each item in the second array, if it's already in the hash, remove it, else add it. At the end you have a hash with two keys, which are your unique elements.

Simple verison in Ruby

def unique(a,b)
  h={}
  a.each do |ax|
    h[ax]=true
  end
  b.each do |bx|
    if h[bx]
      h.delete(bx)
    else
      h[bx]=true
    end
  end
  h.keys
end

With a little more Ruby personality, but still in the universe where we can't simply do (a | b) - (a & b) or a.to_set ^ b.to_set:

def unique(a,b)
  h = {}
  a.each do |ax|
    h[ax] = true
  end
  b.each do |bx|
    h.delete(bx) or h[bx] = true
  end
  h.keys
end