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Problem Set 5: Mispellings


  • Allow you to design and implement your own data structure.
  • Optimize your code’s (real-world) running time.


Create the fastest (real-time) spell-checker possible.


In dictionary.c:

  • Implement load, a function that loads a dictionary into memory via storing words in hash table. Returns true if successful else false.
  • Implement check, a function that returns true if word is in dictionary else false. Case-insensitive.
  • Implement size, a function that returns the number of words in dictionary if loaded else 0 if not yet loaded.
  • Implement unload, a function that unloads dictionary from memory. Returns true if successful else false.

The challenge is to implement load, check, size, and unload as efficiently as possible, in such a way that TIME IN load, TIME IN check, TIME IN size, and TIME IN unload are all minimized. To be sure, it’s not obvious what it even means to be minimized, inasmuch as these benchmarks will certainly vary as you feed speller different values for dictionary and for text. But therein lies the challenge, if not the fun, of this problem set. This problem set is your chance to design. Although we invite you to minimize space, your ultimate enemy is time.

Within the default dictionary are 143,091 words, all of which must be loaded into memory! In fact, take a peek at that file to get a sense of its structure and size. Notice that every word in that file appears in lowercase. From top to bottom, the file is sorted lexicographically, with only one word per line (each of which ends with \n). No word is longer than 45 characters, and no word appears more than once.

So that you can test your implementation of speller, we’ve also provided you with a whole bunch of texts, among them the script from Austin Powers: International Man of Mystery, a sound bite from Ralph Wiggum, three million bytes from Tolstoy, some excerpts from Machiavelli and Shakespeare, the entirety of the King James V Bible, and more.


Left = my code, right = staff solution (time in seconds): 💪

My code vs. staff solution