yutaono

// project euler 28 
//
// The sum of the vertices can be expressed as follows. The w is width of the square.
// 
// sum = (w - 2)^2 + (w - 1) 
// + (w - 2)^2 + 2(w - 1)
// + (w - 2)^2 + 3(w - 1)
// + (w - 2)^2 + 4(w - 1)
// = 4w^2 - 6w + 6
//

yutaono

require 'redis'
require 'hiredis'
 
$redis = Redis.new(
  host: "127.0.0.1",
  port: 6379,
  timeout: 30.0,
  driver: :hiredis
)

yutaono

require 'date'

t1 = DateTime.parse(ARGV[0]) 
t2 = DateTime.parse(ARGV[1])

seconds = ((t2 - t1) * 24 * 60 * 60).to_i
r = seconds.divmod(60)

puts "#{r[0]}min#{r[1]}sec"

yutaono

f1 = 1
f2 = 2
sum = 0

loop {
  break if f2 > 4000000
  sum += f2 if f2 % 2 == 0
  f2 = f1 + f2
  f1 = f2 - f1
}

yutaono

// compile error

import scala.annotation.tailrec

@tailrec
def fib(n: Int): Int = n match {
  case 1 | 2 => 1
  case _ => fib(n - 1) + fib(n - 2)
}

yutaono

trait Monoid[A] {
  def mappend(a: A, b: A): A
  def mzero: A
}

object Monoid {
  implicit val IntMonoid: Monoid[Int] = new Monoid[Int] {
    def mappend(a: Int, b: Int) = a + b
    def mzero = 0
  }

yutaono

trait Greeter {
  val s: String
  def greet(): String = s"greet! $s"
}

object Greeter {
  implicit def convertInt(i: Int): Greeter = new Greeter { val s = i.toString }
}

import Greeter._

yutaono

scala> val a: Option[String] = Some("msg")
a: Option[String] = Some(msg)

scala> <msg content={a orNull} />
warning: there was one feature warning; re-run with -feature for details
res3: scala.xml.Elem = <msg content="msg"/>

scala> val a: Option[String] = None
a: Option[String] = None

yutaono

• Main.scala

import scala.annotation.tailrec

object Main extends App {
  def f(a: Int): Int = {
    a match {
      case x if x <= 1 => 1
      case x => x * f(x - 1)

yutaono

scala> class A[M[_]]
warning: there was one feature warning; re-run with -feature for details
defined class A

scala> class B[M[+_]]
warning: there was one feature warning; re-run with -feature for details
defined class B

scala> class C[M[-_]]
warning: there was one feature warning; re-run with -feature for details