Effective Scala with Project Euler

Solutions to Project Euler problems with explanations of the Scala implementations. Unit tests demonstrate and benchmark the problem solving algorithms. Effective Scala is quick, efficient, and understandable.

Goal: solve the problems efficiently, using Scala effectively. By-products: A library of utilities for solving mathematical problems; examples of the practical applications of mathematics.

How to use this project:

Visit the project euler web site, find a problem that interests you, solve it or try to solve it, write a benchmark test against one of mine, and submit it as a push request. I'll gladly deprecate a solution and leave it as a less-than ideal approach. For an example, see problem_10.

Solved Problems with Commentary:

1-17, 19-26, 28-31, 34-41, 45, 48, 55, 56, 69, 74, 92, 97

Utility classes with unit tests:

Pascal's Triangle
Big Square Root
Sieve of Atkin
Permutation Generator
Spiral Number Grid
Undirected Graph
Unit Fraction
CoinCollection, CoinConstraints, CoinCombination - generate combinations with restrictions
NumberString - convert from digits to alphanumeric spellings and back

Who this project is for:

Intermediate Scala users; you've read Martin Odersky's Programming in Scala, worked through the examples and are hungry for more.
You're interested in functional programming, or looking to expand or transition from procedural or quasi object-oriented programming paradigms.
You may be working on your first real application in Scala.
You're concerned that some of Scala's syntactic sugar and conveniences may cause performance problems when implementing non-trivial algorithms.
You'd like to improve your math skills and see if abstract concepts can give you practical ideas.

History:

I began working on the Project Euler problems in October 2009, with Scala 2.7 and I've updated the code to be compliant with each major release. As Scala versions are promoted to release status, I will update the sources as necessary, and whenever possible change solutions to illustrate and leverage new functionality, e.g. the Scala 2.9.0 release brought the parallel collections functionality and that has been used in the recent solutions (e.g. # 74, 92).