Week 1 Lab: Build a T9 disambiguator

The first lab — turn a keypress sequence into a ranked list of real words, using nothing but a dictionary and a mapping of letters to keys

25 February 2027

Before the lab#

Bring a plain-text word list — any reasonable dictionary file will do — and the standard telephone-keypad letter mapping. You do not need a UI. A function that takes a digit string and returns matching words is the whole assignment.

In the lab#

Twenty minutes on the keypad mapping itself: which letters share a key, and why the historical choices (Q and Z sharing a key with other letters, on phones that predate any standard) still show up in modern implementations. Then work time. By the end, get a sequence like 4663 to return good and home, and have an opinion about which one should come first.

The last ten minutes are a scavenger hunt for keypress collisions your own dictionary produces — pairs of common words that share every key. Two students who find the same collision independently is a good sign your dictionary is a normal one, not an unusual choice you should account for in what you say about the results.

Afterwards#

Nothing here is marked on its own, but this is the version of the problem that Assignment 1’s build should be judged as harder than. If your Assignment 1 submission is easier to build than the twelve-key case, that’s worth noticing before you submit it.