Create a function that accepts an array of words as it's input

Question

Seen this whiteboard challenge online and can't seem to figure it out. HELP!

Create a function that accepts an array of words as it's input.

Your function should return an array of all words that can be typed using letters of the alphabet that are only accessible on a single row of the standard American QWERTY keyboard.

For example:

// given
let words = [ 'sup', 'dad', 'tree', 'snake', 'pet'];
keyboardWords(words);

// return
['dad', 'tree', 'pet'];

And this is how far I've gotten.

const topKeys = ['q', 'w', 'e', 'r', 't', 'y', 'u', 'i', 'o', 'p'];
const middleKeys = ['a', 's', 'd','f', 'g', 'h', 'j', 'k', 'l'];
const buttomKeys = ['z', 'x', 'c', 'v', 'b', 'n', 'm'];

let result = [];

let words = ['sup', 'dad', 'tree', 'snake', 'pet'];

for(let i in words) {
  let eachWord = words[i];

  eachWord.split('').forEach(function(c) {
    console.log(c);
  });

}

I've got to the point where I'm printing each word in the array but dont completly know what method to use to see if each letter in the words in a single array thats topKeys, middle Keys etc...

Answer 1

See Array.prototype.filter(), Set, Spread Syntax, String.prototype.toLowerCase(), and Array.prototype.every() for more info.

// Input.
const input = [
  'ERUT', // top match
  'wdvrmg', // false
  'dsjf', // middle match
  '!^#@&^#', // false
  'CxmvN', // bottom match
  '53454', // false
  '' // false
]

// Match.
const match = (A, B) => [...A].every(x => B.has(x.toLowerCase()))

// Line Words.
const lineWords = words => words.filter(word => word.length && (
  
  // Top match.
  match(word, new Set(['q', 'w', 'e', 'r', 't', 'y', 'u', 'i', 'o', 'p'])) ||
  
  // Middle match.
  match(word, new Set(['a', 's', 'd','f', 'g', 'h', 'j', 'k', 'l'])) ||
  
  // Bottom match.
  match(word, new Set(['z', 'x', 'c', 'v', 'b', 'n', 'm']))
  
))

// Output.
const output = lineWords(input)

// Proof.
console.log(output)

Answer 2

Obviously a lot of ways to do this. My initial reaction would be to make a hash table. I'm not sure it's better than any of the others, but it should perform reasonably and be easy to understand/write on a white board:

const rows = [
  ['q', 'w', 'e', 'r', 't', 'y', 'u', 'i', 'o', 'p'],
  ['a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l'],
  ['z', 'x', 'c', 'v', 'b', 'n', 'm']
];

// make a quick hash
const hash = rows.reduce((acc, row, i) => (row.forEach(letter => acc[letter] = i + 1), acc), {})
let words = ['sup', 'dad', 'tree', 'snake', 'pet', "4545", "", "PoWer", '0'];

let result = []

words.forEach(word => {
  if (!word) return                     // degenerate cases i.e  '', 0, etc.
  let row = hash[word[0].toLowerCase()]
  if (row == undefined) return          // not letters we know about
  for (let i = 1; i < word.length; i++) {
    if (hash[word[i].toLowerCase()] !== row) return
  }
  result.push(word)
})

console.log(result)