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

Here's another possibility. Unlike my previous answer it doesn't modify the arrays passed in, and should have a lower big-O bound (O(n) instead of O(n^2) - assuming constant time hashtable lookups), but will take up significantly more memory.

function findUnique(a:Array, b:Array):Array {
  var aHash:Hashtable = buildHash(a);
  var bHash:Hashtable = buildHash(b);

  var uniqueFromA:int;
  var uniqueFromB:int;

  for each(value:int in a) {
    if(!bHash.contains(value)) {
      uniqueFromA = value;
      break;
    } else {
      /* Not necessary, but will speed up the 2nd for-loop by removing
       * values we know are duplicates. */
      bHash.remove(value);
    }
  }

  for each(value:int in b) {
    if(!aHash.contains(value)) {
      uniqueFromB = value;
      break;
    }
  }

  return [uniqueFromA, uniqueFromB];
}

function buildHash(a:Array):Hashtable {
  var h:Hashtable = new Hashtable();
  for each(value:int in a) {
    h[value] = true;
  }

  return h;
}