Vaguery/pandigital_products.rb

## pandigital_products.rb
require 'pp'
require 'prime'

# for integer p in the given range, find the smallest integer q such that p*q is a pandigital number (has at least one of every digit)

p_range = (1..10)
@digits = (0..9).to_a.collect {|d| d.to_s}

def pandigital?(number)
  number.to_s.chars.uniq.sort == @digits
end

def prime_factors(number)
  decomposition = number.prime_division
  pfactors = []
  decomposition.each do |pf|
    pfactors = pfactors + [pf[0]]*pf[1]
  end
  return pfactors
end

def every_binary(length)
  [true,false].repeated_permutation(length)
end

def split_array(array,mask)
  good = []
  bad = []
  (0...array.length).each do |idx|
    mask[idx] ? (good << array[idx]) : (bad << array[idx])
  end
  return [good,bad]
end

def product(numbers)
  numbers.inject(1,:*)
end

def all_pairs(number)
  pf = prime_factors(number)
  every_binary(pf.length).collect do |mask|
    factors = split_array(pf,mask)
    factors.collect {|f| product(f)}.sort
  end.uniq.sort
end

@discoveries = {}

["0","2","3","4","5","6","7","8","9"].permutation(9).each_with_index do |p,i|
  n = (["1"]+p).join("").to_i
  p "#{n}: #{@discoveries.count}" if (i % 10000 == 0)
  pairs = all_pairs(n)
  pairs.each do |pair|
    idx = pair[0]
    @discoveries[idx] = pair[1] if @discoveries[idx].nil?
  end
end

pp @discoveries.sort
	require 'pp'
	require 'prime'

	# for integer p in the given range, find the smallest integer q such that p*q is a pandigital number (has at least one of every digit)

	p_range = (1..10)
	@digits = (0..9).to_a.collect {\|d\| d.to_s}

	def pandigital?(number)
	number.to_s.chars.uniq.sort == @digits
	end

	def prime_factors(number)
	decomposition = number.prime_division
	pfactors = []
	decomposition.each do \|pf\|
	pfactors = pfactors + [pf[0]]*pf[1]
	end
	return pfactors
	end

	def every_binary(length)
	[true,false].repeated_permutation(length)
	end

	def split_array(array,mask)
	good = []
	bad = []
	(0...array.length).each do \|idx\|
	mask[idx] ? (good << array[idx]) : (bad << array[idx])
	end
	return [good,bad]
	end

	def product(numbers)
	numbers.inject(1,:*)
	end

	def all_pairs(number)
	pf = prime_factors(number)
	every_binary(pf.length).collect do \|mask\|
	factors = split_array(pf,mask)
	factors.collect {\|f\| product(f)}.sort
	end.uniq.sort
	end

	@discoveries = {}

	["0","2","3","4","5","6","7","8","9"].permutation(9).each_with_index do \|p,i\|
	n = (["1"]+p).join("").to_i
	p "#{n}: #{@discoveries.count}" if (i % 10000 == 0)
	pairs = all_pairs(n)
	pairs.each do \|pair\|
	idx = pair[0]
	@discoveries[idx] = pair[1] if @discoveries[idx].nil?
	end
	end

	pp @discoveries.sort