Factorial and Fibonacci in Kotlin

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Here below a little program in Kotlin that implements 2 classes (+ an extra utility Stopwatch class from my previous post http://carlosqt.blogspot.com/2011/05/stopwatch-class-for-java.html). There is the main class, called Fiborial (Fibo(nnacci)+(Facto)rial) that implements the Fibonacci and the Factorial algorithms in two ways, one Recursive (using recursion) and the other Imperative (using loops and states). The second class is just an instance class that does the same thing, but its there just to show the difference between static and instance classes, and finally the third one is the main function which has the execution entry point.

You can also find 3 more little examples at the bottom. One prints out the Factorial's Series and Fibonacci's Series, the second one just shows a class that mixes both: static and instance members (or 2 separate classes in the case of Kotlin since it does not supports staitc methods in a class), and finally the third one that uses different return types (including java.math.BigInteger) for the Factorial method to compare the timing and result.

As with the previous posts, you can copy and paste the code below in your favorite IDE/Editor and start playing and learning with it. This little "working" program will teach you some more basics of the Programming Language.

There are some "comments" on the code added just to tell you what are or how are some features called. In case you want to review the theory, you can read my previous post, where I give a definition of each of the concepts mentioned on the code. You can find it here: http://carlosqt.blogspot.com/2011/01/new-series-factorial-and-fibonacci.html 


The Fiborial Program

// Factorial and Fibonacci in Kotlin
package com.series

import java.math.BigInteger
import com.series.Stopwatch

// Instance (Singleton) Class that works as a Module/Utils class
// static is not a class modifier in Kotlin
object StaticFiborial {
    // 'Static' Field
    private var className : String = "'Static' Constructor"
    // no available static __constructor support
    // Static Initializer Method instead, but need to be explicitly invoked
    fun constructor() {
        className = "'Static' Constructor";
        println(className)
    }
    // 'Static' Method - Factorial Recursive
    fun factorialR(n : Int) : BigInteger? {
        if (n == 1)
            return BigInteger.ONE
        else
            return BigInteger.valueOf(n.toLong())?.multiply(factorialR(n - 1))
    }
    // 'Static' Method - Factorial Imperative
    fun factorialI(var n : Int) : BigInteger? {
        var res: BigInteger? = BigInteger.ONE
        while (n > 1) {
            res = res?.multiply(BigInteger.valueOf(n.toLong()))
            n -= 1
        }
        return res
    }
    // 'Static' Method - Fibonacci Recursive
    fun fibonacciR(n : Int) : Long {
        if (n < 2)
            return 1
        else
            return fibonacciR(n - 1) + fibonacciR(n - 2)
    }
    // 'Static' Method - Fibonacci Imperative
    fun fibonacciI(n : Int) : Long {
        var pre : Long = 1
        var cur : Long = 1
        var tmp : Long
        for (i in 2..n) {
            tmp = cur + pre
            pre = cur
            cur = tmp
        }
        return cur
    }
    // 'Static' Method - Benchmarking Algorithms
    fun benchmarkAlgorithm(algorithm : Int, values : Array<Int>) {
        val timer : Stopwatch = Stopwatch()
        var testValue : Int
        var i : Int = 1
        var facTimeResult : BigInteger? = BigInteger.ZERO
        var fibTimeResult : Long

        when (algorithm) {
            1 -> {
                println("\nFactorial Imperative:");
                // "For" Loop Statement
                for (j in 1..values.size - 1) {
                    testValue = values[j]
                    // Taking Time
                    timer.start()
                    facTimeResult = factorialI(testValue)
                    timer.stop()
                    // Getting Time
                    println(" (${testValue}) = ${timer.getElapsed()}")
                }
            }
            2 -> {
                println("\nFactorial Recursive:")
                // "While" Loop Statement
                while (i < values.size) {
                    testValue = values[i]
                    // Taking Time
                    timer.start()
                    facTimeResult = factorialR(testValue)
                    timer.stop()
                    // Getting Time
                    println(" (${testValue}) = ${timer.getElapsed()}")
                    i += 1
                }
            }
            3 -> {
                println("\nFibonacci Imperative:")
                // "Do-While" Loop Statement
                do {
                    testValue = values[i]
                    // Taking Time
                    timer.start()
                    fibTimeResult = fibonacciI(testValue)
                    timer.stop()
                    // Getting Time
                    println(" (${testValue}) = ${timer.getElapsed()}")
                    i++
                } while (i < values.size)
            }
            4 -> {
                println("\nFibonacci Recursive:")
                // "For Each" Loop Statement
                for (j in values) {
                    testValue = j
                    // Taking Time
                    timer.start()
                    fibTimeResult = fibonacciR(testValue)
                    timer.stop()
                    // Getting Time
                    println(" (${testValue}) = ${timer.getElapsed()}")
                }
            }
            else -> println("DONG!")
        }
    }
}

// Instance Class
// Instance Field
class InstanceFiborial(private var className : String) {
    // Instance Constructor
    this() : this("Instance Constructor") {
        println(this.className)
    }
    // Instance Method - Factorial Recursive
    fun factorialR(n : Int) : BigInteger? {
        // Calling Static Method
        return StaticFiborial.factorialR(n)
    }
    // Instance Method - Factorial Imperative
    fun factorialI(n : Int) : BigInteger? {
        // Calling Static Method
        return StaticFiborial.factorialI(n)
    }
    // Instance Method - Fibonacci Recursive
    fun fibonacciR(n : Int) : Long {
        // Calling Static Method
        return StaticFiborial.fibonacciR(n)
    }
    // Instance Method - Fibonacci Imperative
    fun fibonacciI(n : Int) : Long {
        // Calling Static Method
        return StaticFiborial.fibonacciI(n)
    }
}

fun main(args: Array<String>) {
    println("\n'Static' Class");
    // Calling 'Static' Class and Methods
    // No instantiation needed. Calling method directly from the class
    StaticFiborial.constructor()
    println("FacImp(5) = ${StaticFiborial.factorialI(5)}")
    println("FacRec(5) = ${StaticFiborial.factorialR(5)}")
    println("FibImp(11)= ${StaticFiborial.fibonacciI(11)}")
    println("FibRec(11)= ${StaticFiborial.fibonacciR(11)}")

    println("\nInstance Class");
    // Calling Instance Class and Methods
    // Need to instantiate before using. Call method from instantiated object
    val ff = InstanceFiborial()
    println("FacImp(5) = ${ff.factorialI(5)}")
    println("FacRec(5) = ${ff.factorialR(5)}")
    println("FibImp(11)= ${ff.fibonacciI(11)}")
    println("FibRec(11)= ${ff.fibonacciR(11)}")

    // Create a (generic) list of integer values to test
    // From 5 to 50 by 5
    val values = Array<Int>(11, {i -> i * 5})

    // Benchmarking Fibonacci
    // 1 = Factorial Imperative
    StaticFiborial.benchmarkAlgorithm(1, values)
    // 2 = Factorial Recursive
    StaticFiborial.benchmarkAlgorithm(2, values)

    // Benchmarking Factorial
    // 3 = Fibonacci Imperative
    StaticFiborial.benchmarkAlgorithm(3, values)
    // 4 = Fibonacci Recursive
    StaticFiborial.benchmarkAlgorithm(4, values)

    // Stop and exit
    println("Press any key to exit...")
    //val ins: Scanner = Scanner(System.in)
    //var line: String? = ins.nextLine()
    //ins.close()
}

And the Output is:

Printing the Factorial and Fibonacci Series

package com.series

import java.math.BigInteger
import java.lang.StringBuffer

object Fiborial {
    // Using a StringBuffer as a list of string elements
    fun getFactorialSeries(n : Int) : String? {
        val series = StringBuffer()
        // We begin by concatenating the number you want to calculate
        // in the following format: "!# ="
        series.append("!")
        series.append(n)
        series.append(" = ")
        // We iterate backwards through the elements of the series
        // Reversed ranges are not supported... using while instead
        //for (i in n..0) {
        var i : Int = n
        while (i > 0) {
            // and append it to the list
            series.append(i)
            if (i > 1)
                series.append(" * ")
            else
                series.append(" = ")
            i--
        }
        // Get the result from the Factorial Method
        // and append it to the end of the list
        series.append(factorial(n))
        return series.toString()
    }

    // Using a StringBuffer as a list of string elements
    fun getFibonnaciSeries(n : Int) : String? {
        // Create the String that will hold the list
        val series = StringBuffer()
        // We begin by concatenating the first 3 values which
        // are always constant
        series.append("0, 1, 1")
        // Then we calculate the Fibonacci of each element
        // and add append it to the list
        for (i in 2..n) {
            if (i < n)
                series.append(", ")
            else
                series.append(" = ")
            series.append(fibonacci(i))
        }
        // return the list as a string
        return series.toString()
    }

    fun factorial(n : Int) : BigInteger? {
        if (n == 1)
            return BigInteger.ONE
        else
            return BigInteger.valueOf(n.toLong())?.multiply(factorial(n - 1))
    }

    fun fibonacci(n : Int) : Long {
        if (n < 2)
            return 1
        else
            return fibonacci(n - 1) + fibonacci(n - 2)
    }
}

fun main(args : Array<String>) {
    // Printing Factorial Series
    println("")
    println(Fiborial.getFactorialSeries(5))
    println(Fiborial.getFactorialSeries(7))
    println(Fiborial.getFactorialSeries(9))
    println(Fiborial.getFactorialSeries(11))
    println(Fiborial.getFactorialSeries(40))
    // Printing Fibonacci Series
    println("")
    println(Fiborial.getFibonnaciSeries(5))
    println(Fiborial.getFibonnaciSeries(7))
    println(Fiborial.getFibonnaciSeries(9))
    println(Fiborial.getFibonnaciSeries(11))
    println(Fiborial.getFibonnaciSeries(40))
}

And the Output is:

Mixing Instance and Static Members in the same Class

Normally, instance classes can contain both, instance and static members such as: fields, getters, constructors/initializers, methods, etc. However, In Kotlin, unlike Java, classes do not have static methods, so it doesn't support mixing both of them on the same object or class. In the following code I had to create one Object and one Class to build this example.

package com.series

// 'Static' Class
object StaticFiborial {
    // 'Static' Field/Property
    private var _staticCount : Int = 0
    // 'Static' Read-Only Property
    public val StaticCount : Int
        get() {
            return _staticCount
        }
    // 'Static' Constructor
    //this() : this() {
    // No constructor support for Objects - failed to get descriptor for secondary constructor
    // using an explicit initializer method instead
    fun constructor() {
        println("\nStatic Constructor ${_staticCount}")
    }
    // 'Static' Method
    fun fibonacci(n : Int) {
        _staticCount += 1
        println("\nFibonacci(${n})")
    }
}

// Instance Class
// Instance Field/Property
class InstanceFiborial(private var _instanceCount : Int) {
    // Instance Read-Only Property
    public val InstanceCount : Int
        get() {
            return this._instanceCount
        }
    // Instance Constructor
    this() : this(0) {
        println("\nInstance Constructor ${this._instanceCount}")
    }
    // Instance Method
    fun factorial(n : Int) {
        this._instanceCount += 1
        println("\nFactorial(${n})")
    }
}

fun main(args : Array<String>) {
    // Calling Static Constructor and Methods
    // No need to instantiate
    StaticFiborial.constructor()
    StaticFiborial.fibonacci(5)

    // Calling Instance Constructor and Methods
    // Instance required
    val fib = InstanceFiborial()
    fib.factorial(5)

    StaticFiborial.fibonacci(15)
    fib.factorial(5)

    // Calling Instance Constructor and Methods
    // for a second object
    val fib2 = InstanceFiborial()
    fib2.factorial(5)

    println("")
    // Calling Static Property
    println("Static Count = ${StaticFiborial.StaticCount}")
    // Calling Instance Property of object 1 and 2
    println("Instance 1 Count = ${fib.InstanceCount}")
    println("Instance 2 Count = ${fib2.InstanceCount}")
}

And the Output is:

Factorial using java.lang.Long, java.lang.Double, java.math.BigInteger

package com.series

import java.math.BigInteger
import com.series.Stopwatch

// Long Factorial
fun factorialInt64(n : Int) : Long {
    if (n == 1)
        return 1
    else
        return n * factorialInt64(n - 1)
}

// Double Factorial
fun factorialDouble(n : Int) : Double {
    if (n == 1)
        return 1.0
    else
        return n * factorialDouble(n - 1)
}

// BigInteger Factorial
fun factorialBigInteger(n : Int) : BigInteger? {
    if (n == 1)
        return BigInteger.ONE
    else
        return BigInteger.valueOf(n.toLong())?.multiply(factorialBigInteger(n - 1))
}

fun main(args: Array<String>) {
    val timer = Stopwatch()
    var facIntResult : Long = 0
    var facDblResult : Double = 0.0
    var facBigResult = BigInteger.ZERO

    println("\nFactorial using Int64")
    // Benchmark Factorial using Int64
    var i = 5
    while (i < 55) {
        timer.start()
        facIntResult = factorialInt64(i)
        timer.stop()
        println(" (${i}) = ${timer.getElapsed()} : ${facIntResult}")
        i += 5
    }
    println("\nFactorial using Double")
    // Benchmark Factorial using Double
    i = 5
    while (i < 55) {
        timer.start()
        facDblResult = factorialDouble(i)
        timer.stop()
        println(" (${i}) = ${timer.getElapsed()} : ${facDblResult}")
        i += 5
    }
    println("\nFactorial using BigInteger")
    // Benchmark Factorial using BigInteger
    i = 5
    while (i < 55) {
        timer.start()
        facBigResult = factorialBigInteger(i)
        timer.stop()
        println(" (${i}) = ${timer.getElapsed()} : ${facBigResult}")
        i += 5
    }
}

And the Output is: