5kyu_CommonDenominators.js

// 5 kyu - Common Denominators

// Description:
// Common denominators
// You will have a list of rationals in the form
//  [ [numer_1, denom_1] , ... [numer_n, denom_n] ]
// where all numbers are positive ints.
// You have to produce a result in the form
//  (N_1, D) ... (N_n, D)
// in which D is as small as possible and
//  N_1/D == numer_1/denom_1 ... N_n/D == numer_n,/denom_n.
// Example :
//  [ [1, 2], [1, 3], [1, 4] ] produces the string (6,12)(4,12)(3,12)

let gcd = function(a, b) {
  if(!b) { return a; }
  return gcd(b, a % b);
}

let lcm = function(d1, d2) {
  return d1 * d2 / gcd(d1, d2);
}

let convertFrac = function(arr) {
  let denom = arr.reduce((a, b) => lcm(b[1], a), 1);
  return arr.map(a => `(${a[0]*(denom/a[1])},${a[1] * (denom/a[1])})`).join('');
}