It is refreshing to see a data structure "explained" without a drawing of some boxes and arrows. +1 there for the creativity -- I'd be even more pleased to see a data structure explained with words without relying on images at all.

Also:

  ...to check if a word exists in the text file, it takes
  at most, as many operations as the length of the word
  itself. Much better than the 235,887 operations it
  was going to take before.

But your source for the words (/usr/share/dict/words) is probably already sorted! I don't think that's a fair upper bound to quote.