12-224606.scala

class Rational(n: Int = 1, d: Int = 1) {
  private def gcd(x: Int, y: Int): Int = {
    if (x == 0) y
    else if (x < 0) gcd(-x, y)
    else if (y < 0) -gcd(x, -y)
    else gcd(y % x, x)
  }
  private val g = gcd(n, d)
  val numer: Int = n/g
  val denom: Int = d/g
  def +(that: Rational) =
    new Rational(numer * that.denom + that.numer * denom,
    denom * that.denom)
  def -(that: Rational) =
  new Rational(numer * that.denom - that.numer * denom,
    denom * that.denom)
  def *(that: Rational) =
    new Rational(numer * that.numer, denom * that.denom)
  def /(that: Rational) =
    new Rational(numer * that.denom, denom * that.numer)
  override def toString(): String = s"${n} % ${d}"
}

val a = new Rational(1, 5)
val b = new Rational(3, 15)
val c = new Rational(3, 3)
val d = new Rational(1)
println(a)
println(b)
println(c)
println(d)