euler/crystal/euler.cr

# miscellaneous stuff

require "big"

module Euler
  extend self

  alias NumType = Int32 | Int64 | UInt32 | UInt64

  macro trial_division_method(given_type)
    def trial_division(n : {{given_type}})
      factors = [] of {{given_type}}
      check = ->(p: {{given_type}}) {
        q, r = n.divmod(p)
        while r.zero?
          factors << p
          n = q
          q, r = n.divmod(p)
        end
      }

      check.call(2)
      check.call(3)
      p = 5
      while p * p <= n
        check.call(p)
        p += 2
        check.call(p)
        p += 4
      end
      factors << n if n > 1
      factors
    end
  end

  trial_division_method(NumType)
  trial_division_method(BigInt)

  def prime_factorization(n : NumType | BigInt)
    result = {} of (NumType | BigInt) => Int32
    factors = self.trial_division(n)

    factors.each do |f|
      result[f] = 0
      num = n
      while num % f == 0
        result[f] += 1
        num /= f
      end
    end

    result
  end

  def to_big_ints(num_list : Array(NumType))
    num_list.map { |n| BigInt.new(n) }
  end

  def to_digit_list(n : NumType | BigInt)
    n.to_s.chars.map { |d| d.to_i }
  end

  def palindrome?(x)
    x.to_s.reverse == x.to_s
  end
end