The textbook solution I assume you meant, to find the most common k elements of a list, uses an updatable priority queue (heap). This orders the (key, count) pa

The textbook solution I assume you meant, to find the most common k elements of a list, uses an updatable priority queue (heap). This orders the (key, count) pairs by the count. But that's a separate question from how you look up the key (i.e. given a word, find the pair whose count you want to increment), which is what Knuth's hash tries were for here.