« Boston Python puzzles

Phone Numbers

Long, long ago, people used to memorize phone numbers. To help people do this, telephone keypads included letters. Here is a typical encoding:

        1       2       3
               abc     def

        4       5       6
       ghi     jkl     mno

        7       8       9
       pqrs    tuv     wxyz

        *       0       #

1. Write a program that generates Boston vanity telephone numbers (1-617-XXX-XXXX), where XXX-XXXX encodes a person's name.

For example, the vanity number for 'Adriana' would be 1-617-237-4262, which is 1-617-ADRIANA.

But what to do with names longer or shorter than 7 letters? If a name is shorter, then the vanity number will begin with a padding of 7's. For example, the vanity number for 'Adam' would be 1-617-777-2326, which is 1-617-777-ADAM. If a name is longer than 7 letters, then the vanity number will drop all interior vowels starting from the end. For example, the vanity number for 'Elizabeth' would be 1-617-354-9284 (for 1-617-ELIZBTH). And for crazy long names, you just take the first 4 letters and the last 3. For example, 'Mahershalalhashbaz' (yes that's a real name) would be 1-617-624-3229 (for 1-617-MAHEBAZ).

2. Now write a program that does the reverse, taking a vanity telephone number and revealing the name. Impossible, you say? Not quite.

You could at least encode the first 3 letters of a name. A simple system for achieving this would convert the old keypad number-letter mapping into a list of tuples like this:

ADR = [(2,0), (3,0), (7,2)]

The first numbers of each tuple is the keypad number, and the second is the index of the correct letter under the keypad number.

But that system only uses 6 of your 7 telephone digits (wasting entropy), and can't we do better than a 3-letter name encoding? (Hint: yes we can, here's one way.)