Solutions for Project Euler Problems 1 to 3 in Kotlin

Tada!! It is Kotlin!

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In this article, I shall tell you about a few puzzles in Kotlin along with the solutions. These questions came from the Project Euler website:

About - Project Euler

Before solving problems, we will create a Base class for our solution classes:

abstract class Solution {
    abstract fun solve()
}

Also, here is our Main class:

class Main {
    companion object {
        @JvmStatic
        fun main(a: Array<String>) {
            //Replace `1` with Solution's class name 
            `1`().solve()
        }
    }
}

#1. Multiples of 3 and 5

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6, and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

Here is the solution:

class `1` : Solution() {
    override fun solve() {
        //We first initialise variable sum
        var sum = 0
        //We run a loop from 1 to one less than 1000 (999)
        for(i in 1..999) {
            //If i is divisible by 3 or 5 then we add it to variable sum
            if (i%3 == 0 || i%5== 0) {
                sum+=i
            }
        }
        //We print the sum variable
        println(sum)
    }
}

Answer: 233168

#2. Even Fibonacci numbers

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

Here is the awesome solution:

class `2` : Solution() {
    override fun solve() {
        //We first create variables for Fibonacci series
        var first = 0
        var second = 1
        //We will store result here
        var sum = 0
        //We create a loop
        while (first + second < 4000000) {
            val third = first + second
            if (third % 2 == 0) {
             //If the value of variable third is even then we add it to sum
                sum += third
            }
            //We reassign first and second for next fibonacci number
            first = second
            second = third
        }
        println("Sum: $sum")
    }
}

Answer: 233168

#3. Largest prime factor

The prime factors of 13195 are 5, 7, 13, and 29. What is the largest prime factor of the number 600851475143?

class `3` : Solution() {
    companion object {
        //We create compile time constant "NUM"
        const val NUM = 600851475143
    }

    override fun solve() {
        //Now, we need not to create loop for more than
        // half of the number. Also, we start with 3
        // since NUM is odd number and take step as 2 since
        //it will never be divisible by 2.
        for (i in 3..NUM / 2 step 2) {
            //We skip for basic numbers 3, 5 and 7
            if (i % 3 == 0L || i % 5 == 0L || i % 7 == 0L) {
                continue
            }
            if (NUM % i == 0L) {
                if (isPrime(i)) {
                    println("\n$i is prime and divides that no.")
                }
            }
        }
    }

    /**
     * If [num] is prime then return true. Return
     * false otherwise.
     */
    private fun isPrime(num: Long): Boolean {
        for (i in 2..num / 2) {
            if (num % i == 0L) {
                return false
            }
        }
        return true
    }
}

Answer: 6857

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