Words On A Telephone Keypad
January 13, 2017
We begin with a function that computes the signature of a word, ignoring non-letters:
(define (sign str) ; telephone keyboard A B C D E F G H I J K L M N O P Q R S T U V W X Y Z (define keys (vector 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 7 8 8 8 9 9 9 9)) (define (lookup c) (vector-ref keys (- (char->integer c) 65))) (undigits (map lookup (filter char-alphabetic? (string->list (string-upcase str))))))
> (sign "act") 228 > (sign "bat") 228 > (sign "cat") 228 > (sign "can't") 2268 > (sign "PRAXIS") 772947
We use a hash table to store the words; the insert function adds a word to a list of words with the same signature, and the lookup function returns a possibly-empty list of words with the requested signature:
(define table (make-hash (lambda (x) x) = (list) 997)) (define (insert word) (table 'update! (sign word) (lambda (key words) (cons word words)) (list word))) (define (lookup signature) (sort string<? (table 'lookup signature)))
Building a table from a list of words is easy, just say (for-each insert words). To build a table from a file containing one word per line, using our library for processing text files, say:
(for-each-port read-line insert file-name)
Once the table is built, you can query it like this:
> (lookup 228)
("act" "bat" "cat")
> (lookup 2268)
("can't")
> (lookup 772947)
("praxis")
> (lookup 12345)
()
You can run the program at http://ideone.com/JiwqfI.
Programming Praxis 
Here’s one that goes the other way, turning the provided number into a string regex, and then using grep to search /usr/share/dict/words (via a Kawa process quasi-literal).
(import (srfi 13)) ; for string-join (require 'regex) ; for regex-split (define letters ["[+]" "1" "[abc]" "[def]" "[ghi]" "[jkl]" "[mno]" "[pqrs]" "[tuv]" "[wxyz]"]) (define (digits n::integer) (let loop ((ds '()) (n n)) (if (< n 10) (cons n ds) (loop (cons (remainder n 10) ds) (div n 10))))) (define (num->regex n::integer) (string-join (map letters (digits n)) "")) (define (paragraph->lines s::String) (regex-split #/\n/ (*:trim s))) (define (lookup n::integer) (paragraph->lines &`{grep -i "^&[(num->regex n)]$" /usr/share/dict/words})) (for-each (lambda (arg) (format #t "~a: ~a~%" arg (lookup (string->number arg)))) (cdr (command-line)))$ kawa /tmp/words.scm 772947 228
772947: (praxis)
228: (Abu abu act Bat bat Cat cat)
@Jamie: Great idea! Here’s a node.js version:
const readline = require('readline'); const s = process.argv[2] || "43556"; const map = ['[+]','1','[abc]','[def]','[ghi]','[jkl]','[mno]','[pqrs]','[tuv]','[wxyz]']; let restr = ""; for (const c of s.split('')) { restr += map[Number(c)] || ""; } restr = "^" + restr + "$"; // Match whole line const re = new RegExp(restr,"i"); // Case insensitive const rl = readline.createInterface({ input: process.stdin; }); rl.on('line', function(line){ if (re.test(line)) console.log(line); })A solution in bash.