antimon2

require 'prime'
class Prime
  def twins n = nil
    return to_enum :twins, n unless block_given?
    each(n).each_cons(2) do |p1, p2|
      yield [p1, p2] if p2 - p1 == 2
    end
  end
end

antimon2

require 'prime'
class Prime
  def cosins n = nil
    return to_enum :cosins, n unless block_given?
    yield [3, 7]
    each(n).each_cons(2) do |p1, p2|
      yield [p1, p2] if p2 - p1 == 4
    end
  end
end

antimon2

# original: http://log.ttsky.net/article/19515687.html
require 'prime'

class Prime

  # An implementation of +Prime::PseudoPrimeGenerator+.
  class A2Generator < PseudoPrimeGenerator
    def initialize
      @h = {}
      @n = nil

antimon2

# original: Prime::EratosthenesGenerator and Prime::EratosthenesSieve
require 'prime'
require 'singleton'

class Prime

  # An implementation of +Prime::PseudoPrimeGenerator+.
  #
  # Uses +A2ESieve+.
  class A2EGenerator < PseudoPrimeGenerator

antimon2

# -*- coding: utf-8 -*-
# morphological.rb
# original: morphological.py (http://gihyo.jp/dev/serial/01/machine-learning/0003)

require 'MeCab'

module Morphological
  def split sentence
    mecab = MeCab::Tagger.new
    node = mecab.parseToNode sentence

antimon2

def sq? n
  # ↓32bit整数の範囲ならとりあえずこれでOK
  Math.sqrt(n).round**2 == n
end

def project_euler_45 n=143
  loop do
    n += 1
    h = n * (2 * n - 1)
    next unless sq?(8 * h + 1)

antimon2

require 'prime'

def project_euler_46
  Prime.each_cons(2) do |p1, p2|
    (p1 + 2).step(p2 - 2, 2) do |n|
      return n unless (1..Math.sqrt((n-3)/2)).find{|m|(q = n - 2*m*m).prime?}
    end
  end
end

antimon2

require 'prime'

def project_euler_47 n=4
  return if n < 2
  Prime.each_cons(2) do |p1, p2|
    nums = ((p1+1)...p2).select{|m|m.prime_division.size==n}
    idx = 0.upto(nums.size-n).find{|i|nums[i+n-1]==nums[i]+n-1}
    return nums[idx] if idx
  end
end

antimon2

def project_euler_68
  res = 0
  arr = (1..9).to_a
  arr.combination(5) do |(*inner)|
    s = inner.inject(&:+)
    next unless s % 5 == 0
    t = s.div(5) + 11
    outer = (arr - inner) << 10
    o_min = outer.min
    inner.combination(2) do |a, b|

antimon2

require 'prime'

class Integer
  def phi
    self.prime_division.inject(1){|m,(p,k)|m*=p**k-p**(k-1)}
  end
  def phi_ratio
    self.to_f / self.phi
  end
end