Given an array of items (in this case, just strings and integers, though your program should be able to handle booleans and floats as well), run through the array and then return an array of the items that appear only once in the original array.
For example, given [1, 2, "three", "three", 4], we should get back [1, 2, 4].
You may find it worthwhile to use the Ruby array class documentation, but know that there is no single method (that already exists) that can solve this for you, and that you can solve this problem without using any of the fancier array methods.