In class and in the reading, we saw various algorithms for sorting an array of ints. The fastest ones -- among those whose base operation is to compare two elements -- ran in time O(N log N). In fact, unless you know something more about your data, you can't have a faster sorting algorithm.
Suppose you want to sort an array of doubles, and you know the following fact: while the array has N doubles, there are only O(log N) distinct values within the array. Use this information to sort the array in time O(n log(log N)). While it is possible to write an algorithm that guarantees this running time, for purposes of this problem, it is enough to have that time in expectation.