valid-bst 40 min tree-manager 1 day
haskell standard libraries used by hackerrank base-prelude, logict, pipes, hashtables, random, text, vector, aeson, lens, lens-aeson, split, bytestring, array, arrow-list, regex-applicative, regex-base, regex-compat, regex-pcre-builtin, regex-posix, regex-tdfa, generic-aeson, parsec, unordered-containers, attoparsec, comonad, deepseq, dlist, either, matrix, MemoTrie, threads, monad-memo, memoize, base-unicode-symbols, basic-prelude, bifunctors