Rational.kt

package rationals

import java.math.BigInteger

data class Rational(val n: BigInteger, val d: BigInteger): Comparable<Rational> {

    init { require(d != BigInteger.ZERO ) {"Zero is not allowed in the denominator"} }

    override fun toString(): String {
        if (this.d == BigInteger.ONE) return "${this.n}"
        return "$n/$d"
    }

    override fun compareTo(other: Rational): Int {
        return n.times(other.d).compareTo(other.n.times(d))
    }

}

fun String.toRational(): Rational = if (this.contains("/")) {
    val split = this.split("/")
    val n = split[0].toBigInteger()
    val d = split[1].toBigInteger()

    // normalize
    val g = n.gcd(d)
    val num = n / g
    val den = d / g

    if(den < BigInteger.ZERO)
        Rational(-num, den.abs())
    else
        Rational(num, den)
} else {
    Rational(this.toBigInteger(), BigInteger.ONE)
}

infix fun Int.divBy(d: Int): Rational = Rational(this.toBigInteger(), d.toBigInteger()).toString().toRational()

infix fun Long.divBy(d: Long): Rational = Rational(this.toBigInteger(), d.toBigInteger()).toString().toRational()

infix fun BigInteger.divBy(d: BigInteger): Rational = Rational(this, d).toString().toRational()

operator fun Rational.unaryMinus(): Rational = Rational(-this.n, this.d)

operator fun Rational.plus(other: Rational): Rational {
    return if (this.d == other.d) {
        val n = this.n + other.n
        val d = this.d
        Rational(n, d).toString().toRational()
    } else {
        val d = this.d * other.d
        val na = this.n * other.d
        val nb = other.n * this.d
        val n = na + nb
        Rational(n, d).toString().toRational()
    }
}

operator fun Rational.minus(other: Rational): Rational {
    return if (this.d == other.d) {
        val n = this.n + other.n
        val d = this.d
        Rational(n, d).toString().toRational()
    } else {
        val d = this.d * other.d
        val na = this.n * other.d
        val nb = other.n * this.d
        val n = na - nb
        Rational(n, d).toString().toRational()
    }
}

operator fun Rational.times(other: Rational): Rational =
    Rational(this.n * other.n, this.d * other.d).toString().toRational()

operator fun Rational.div(other: Rational): Rational {
    val n = this.n * other.d
    val d = this.d * other.n
    return Rational(n, d).toString().toRational()
}