numeric-keyword-words.js

const fs = require("fs");

const letterToNumber = {
  a: 2,
  b: 2,
  c: 2,
  d: 3,
  e: 3,
  f: 3,
  g: 4,
  h: 4,
  i: 4,
  j: 5,
  k: 5,
  l: 5,
  m: 6,
  n: 6,
  o: 6,
  p: 7,
  q: 7,
  r: 7,
  s: 7,
  t: 8,
  u: 8,
  v: 8,
  w: 9,
  x: 9,
  y: 9,
  z: 9,
};

const numberToLetters = {
  2: "abc".split(""),
  3: "def".split(""),
  4: "ghi".split(""),
  5: "jkl".split(""),
  6: "mno".split(""),
  7: "pqrs".split(""),
  8: "tuv".split(""),
  9: "wxyz".split(""),
};

const wordToNumber = (word) =>
  word
    .toLowerCase()
    .split("")
    .map((l) => `${letterToNumber[l]}`)
    .join("");

const wordToNumber_ = (word) =>
  word
    .toLowerCase()
    .split("")
    .reduce((acc, l) => `${acc}${letterToNumber[l]}`, "");

console.log("--- Word to number ----\n");

console.log(wordToNumber("adeg"));
console.log(wordToNumber_("adeg"));

console.log();

// -----------------------------------------------------------------------------

console.log("--- Number to words ---\n");

// O(n)
const englishWords = new Set(
  fs
    // Mac OS
    .readFileSync("/usr/share/dict/words", "utf8")
    .split("\n")
    .map((word) => word.toLowerCase())
);

console.log("ENGLISH WORDS COUNT:", englishWords.size);
console.log();

const flatten = (xss) => [].concat(...xss);

// O(n * m)
const allPairsWith = (f) => (as, bs) =>
  flatten(as.map((a) => bs.map((b) => f(a, b))));

const append = (a, b) => `${a}${b}`;

const numberToWords = (num) => {
  // Array.map    -> O(n)
  // String.split -> O(n)
  const letters = num.split("").map((n) => numberToLetters[n]);

  const combinations = letters
    .slice(1)
    .reduce((acc, ls) => allPairsWith(append)(acc, ls), letters[0] || []);

  return combinations;
};

console.log({
  23: numberToWords("23").length,
  234: numberToWords("234").length,
  237: numberToWords("237").length,
  9987: numberToWords("9987").length,
});

const numberToValidWords = (words) =>
  // Array.filter -> O(n)
  // Set.has      -> O(1)
  words.filter((word) => englishWords.has(word));

console.log(numberToValidWords(numberToWords("23")));

console.time("Holland");

const holland = wordToNumber_("Holland");

console.log("Holland: ->", holland);

console.log(holland, "->", numberToValidWords(numberToWords(holland)));

console.timeEnd("Holland");