From: incag neato <lists@...>
Date: 2012-10-07T06:40:08+09:00
Subject: Kata @$$-kick! Prime Factors

I'm trying to re-write the prime factors kata without using the Prime
library. About to go berserk with frustration, too.

I've tried a mess of different techniques and puts'd all over the place
to "see" a solution, but have just been looking at it too long now.

Right now the code below will iterate over a range, find the factors,
and add
to array.

But I'm missing something to reduce the factors to actual prime factors.
: \

The following produces the answer I'm looking for, with the prime
library (for
guidance).

require 'prime'

def prime(n)
  n.prime_division.map { |base, exp| [base]*exp }.flatten
end

Any input on the below?? Thanks in advance for your time & help

# -----------
# Create a method which takes integers and returns their prime factors
in an array.

  # primes are integers greater than 1,
  # divisible only by 1 and themselves.
  # primes > 2 are odd numbers.
  # prime factors of integer <= square root of integer parameter (n)

def primes(n)
puts
puts
  # initialize the array to add the prime factors
  prime_factors = []
  factor = n

  # iterate over range, up to sqrt integer
  (2).upto(Math.sqrt(factor).to_i). each do |divisor|
  # for divisor in (2..factor) do
  # Math.sqrt(factor).to_i.downto(2).each do |divisor|

    puts "Finding primes from #{divisor} to #{factor}."
    puts
    puts "Checking now if #{divisor} is a factor."

      if factor % divisor == 0

        puts "--> #{factor} is divisible by #{divisor}."

        prime_factors << divisor

        puts "Factors array now set: #{prime_factors.inspect}"

        quotient = factor / divisor

        factor = quotient

      end #/if loop

  end #/do
  puts
  puts "Exiting loop; #{factor} is the last quotient to've passed if
statement."
  prime_factors << factor
  p prime_factors
end

# primes(256) # should print [2,2,2,2,2,2,2,2]
# primes(100) # should print [2,2,5,5]
# primes(81) # should print [3,3,3,3]
# primes(10) # should print [2,5]
primes(8) # should print [2,2,2] --> currently prints [2,4]

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