Problem 4 in Scala

/**
  * Largest palindrome product: https://projecteuler.net/problem=4
  *
  * TA palindromic number reads the same both ways. The largest
  * palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
  *
  * Find the largest palindrome made from the product of two 3-digit numbers.
  */

val allnum = 100 to 999
val allprod = for (x <- allnum; y <- allnum) yield {(x, y, x * y)}
val answer = allprod.
  filter(x => (x._3 == x._3.toString.reverse.toInt)).
  sortWith(_._3 > _._3).head

Problem 3 in Scala

/**
  * Largest prime factor: https://projecteuler.net/problem=3
  *
  * The prime factors of 13195 are 5, 7, 13 and 29.
  *
  * What is the largest prime factor of the number 600851475143?
  */

import scala.math._

def isPrime(n: Int) = (2 to math.sqrt(n).toInt).forall(n%_ != 0)

val n = 600851475143L
val answer = 1.to(sqrt(n).toInt).filter(isPrime).filter(n % _ == 0).sortWith(_ > _).head

Problem 2 in Scala

/**
  * Even Fibonacci numbers: https://projecteuler.net/problem=2
  *
  * 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.
  */

import scala.collection.mutable.ListBuffer

val n = 4000000
var newElement = 0
val fibList = ListBuffer(1,2)
while (newElement <= n) {
val a = fibList.length
newElement = fibList(a - 1) + fibList(a - 2)
if (newElement <= n) fibList.append(newElement)
}

val answer = fibList.filter(_ % 2 == 0).sum

Problem 1 in Scala

/**
  * Multiples of 3 and 5: https://projecteuler.net/problem=1
  *
  * 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.
  */

val n = 1000
val answer = 1.until(n).filter(x => (x % 3 == 0 || x % 5 == 0)).sum