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Scala: Project Euler problem 2

by Gregor Uhlenheuer on July 17, 2012

There you go, the second problem of Project Euler:

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.

class Euler002 extends Euler {

  def number = 2

  def solution = {

    lazy val sequence = {
      def build(i : Int, j : Int) : Stream[Int] = i #:: build(j, i+j)
      build(1, 2)
    }

    val fibs = for (elem <- sequence.iterator if elem % 2 == 0) yield elem
    fibs.takeWhile(_ <= 4000000).sum
  }
}

This solution uses a lazily evaluated sequence (Stream) where each element is computed as it is requested.

This post is tagged with euler, scala and programming