Hash index point lookup

Build a hash index over a table and answer point lookups. You are given rows as [key, value] pairs (keys are strings, not unique, later rows with the same key shadow earlier ones, last-write-wins) and a list of lookup keys. Build the index once, then for each lookup key return its current value, or the string "MISS" if the key is absent. Return a list of values, one per lookup, in order.