luke20.js

console.time('luke20')

var sets = {}, size = 0

var sum = function (x, y) {
  var num = Math.abs(x).toString() + Math.abs(y)
  return parseInt(eval(num.replace(/(\d)(?=\d)/g, '$1+')))
}

var check = function (x, y) {
  if (sets[x+','+y] || sum(x, y) > 19) {
    return
  }

  sets[x+','+y] = 1

  check(x + 1, y)
  check(x - 1, y)
  check(x, y + 1)
  check(x, y - 1)
}

check(0, 0)


for (var key in sets) {
  if (sets.hasOwnProperty(key)) size++;
}
console.log(size)

console.timeEnd('luke20')