Top k frequent tags

A photo library shows its most-used tags first. Given the list of every tag application (repeats meaningful) and an integer k (k >= 1), return the k most frequently used distinct tags. Order the result by frequency, highest first; break frequency ties alphabetically (lexicographically ascending). If fewer than k distinct tags exist, return them all under the same ordering. For example, tags ["pop", "rock", "pop", "jazz", "rock", "pop"] with k = 2 give ["pop", "rock"], and ["t", "t", "s", "s", "r"] with k = 1 gives ["s"].