I've resorted to starting with "find the greatest int in an array of ints". And yes, I'm routinely disappointed.
Easy -- quicksort! :-)
Actually, if their solution is bit luke-warm, I often follow up with 'now find the second greatest int'. Those that don't consider sorting the array go in the big pile. :)
I'm curious why you'd choose an algorithm that on average takes O(n log n) comparisons with a O(n^2) worst case versus simply iterating O(n)?
Unless there are other requirements I don't see why you'd suggest sorting the elements.
I certainly wouldn't choose that algorithm. I thought the correct solution was obvious enough that I could joke about it...