Re: Kata @$$-kick! Prime Factors

This will get you the answers you want BUT it is not doing the correct
thing.
Your trial divisors only need to be primes.

# -----------
# 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
  divisor = 2
  while divisor*divisor <= factor
  # 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."

      while 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
      divisor += 1

  end #/do
  puts
  puts "Exiting loop; #{factor} is the last quotient to've passed if
statement."
  if factor > 1
      prime_factors << factor
   end
  p prime_factors
end


On Sat, Oct 6, 2012 at 4:40 PM, incag neato <[e-mail]> wrote:

> 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]
>
> --
> Posted via http://www.ruby-forum.com/.
>
>


-- 
David N. Springer
Eau Claire, WI