From: David Springer <dnspringer@...>
Date: 2012-10-07T10:29:31+09:00
Subject: Re: Kata @$$-kick! Prime Factors

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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 <lists@ruby-forum.com> 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

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This will get you the answers you want BUT it is not doing the correct thin=
g.<div>Your trial divisors only need to be primes.</div><div><br></div><div=
><div># -----------</div><div># Create a method which takes integers and re=
turns their prime factors in an array.</div>
<div><br></div><div>=A0 # primes are integers greater than 1,</div><div>=A0=
 # divisible only by 1 and themselves.</div><div>=A0 # primes &gt; 2 are od=
d numbers.</div><div>=A0 # prime factors of integer &lt;=3D square root of =
integer parameter (n)</div>
<div><br></div><div>def primes(n)</div><div>puts</div><div>puts</div><div>=
=A0 # initialize the array to add the prime factors</div><div>=A0 prime_fac=
tors =3D []</div><div>=A0 factor =3D n</div><div>=A0 divisor =3D 2</div><di=
v>=A0 while divisor*divisor &lt;=3D factor</div>
<div>=A0 # iterate over range, up to sqrt integer</div><div>=A0 #(2).upto(M=
ath.sqrt(factor).to_i). each do |divisor|</div><div>=A0 # for divisor in (2=
..factor) do</div><div>=A0 # Math.sqrt(factor).to_i.downto(2).each do |divi=
sor|</div>
<div><br></div><div>=A0 =A0 puts &quot;Finding primes from #{divisor} to #{=
factor}.&quot;</div><div>=A0 =A0 puts</div><div>=A0 =A0 puts &quot;Checking=
 now if #{divisor} is a factor.&quot;</div><div><br></div><div>=A0 =A0 =A0 =
while factor % divisor =3D=3D 0</div>
<div><br></div><div>=A0 =A0 =A0 =A0 puts &quot;--&gt; #{factor} is divisibl=
e by #{divisor}.&quot;</div><div><br></div><div>=A0 =A0 =A0 =A0 prime_facto=
rs &lt;&lt; divisor</div><div><br></div><div>=A0 =A0 =A0 =A0 puts &quot;Fac=
tors array now set: #{prime_factors.inspect}&quot;</div>
<div><br></div><div>=A0 =A0 =A0 =A0 quotient =3D factor / divisor</div><div=
><br></div><div>=A0 =A0 =A0 =A0 factor =3D quotient</div><div><br></div><di=
v>=A0 =A0 =A0 end #/if loop</div><div>=A0 =A0 =A0 divisor +=3D 1</div><div>=
<br></div><div>=A0 end #/do</div>
<div>=A0 puts</div><div>=A0 puts &quot;Exiting loop; #{factor} is the last =
quotient to&#39;ve passed if statement.&quot;</div><div>=A0 if factor &gt; =
1</div><div>=A0 =A0 =A0 prime_factors &lt;&lt; factor</div><div>=A0 =A0end<=
/div><div>=A0 p prime_factors</div>
<div>end</div><div><br></div><br><div class=3D"gmail_quote">On Sat, Oct 6, =
2012 at 4:40 PM, incag neato <span dir=3D"ltr">&lt;<a href=3D"mailto:lists@=
ruby-forum.com" target=3D"_blank">lists@ruby-forum.com</a>&gt;</span> wrote=
:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">I&#39;m trying to re-write the prime factors=
 kata without using the Prime<br>
library. About to go berserk with frustration, too.<br>
<br>
I&#39;ve tried a mess of different techniques and puts&#39;d all over the p=
lace<br>
to &quot;see&quot; a solution, but have just been looking at it too long no=
w.<br>
<br>
Right now the code below will iterate over a range, find the factors,<br>
and add<br>
to array.<br>
<br>
But I&#39;m missing something to reduce the factors to actual prime factors=
.<br>
: \<br>
<br>
The following produces the answer I&#39;m looking for, with the prime<br>
library (for<br>
guidance).<br>
<br>
require &#39;prime&#39;<br>
<br>
def prime(n)<br>
=A0 n.prime_division.map { |base, exp| [base]*exp }.flatten<br>
end<br>
<br>
Any input on the below?? Thanks in advance for your time &amp; help<br>
<br>
# -----------<br>
# Create a method which takes integers and returns their prime factors<br>
in an array.<br>
<br>
=A0 # primes are integers greater than 1,<br>
=A0 # divisible only by 1 and themselves.<br>
=A0 # primes &gt; 2 are odd numbers.<br>
=A0 # prime factors of integer &lt;=3D square root of integer parameter (n)=
<br>
<br>
def primes(n)<br>
puts<br>
puts<br>
=A0 # initialize the array to add the prime factors<br>
=A0 prime_factors =3D []<br>
=A0 factor =3D n<br>
<br>
=A0 # iterate over range, up to sqrt integer<br>
=A0 (2).upto(Math.sqrt(factor).to_i). each do |divisor|<br>
=A0 # for divisor in (2..factor) do<br>
=A0 # Math.sqrt(factor).to_i.downto(2).each do |divisor|<br>
<br>
=A0 =A0 puts &quot;Finding primes from #{divisor} to #{factor}.&quot;<br>
=A0 =A0 puts<br>
=A0 =A0 puts &quot;Checking now if #{divisor} is a factor.&quot;<br>
<br>
=A0 =A0 =A0 if factor % divisor =3D=3D 0<br>
<br>
=A0 =A0 =A0 =A0 puts &quot;--&gt; #{factor} is divisible by #{divisor}.&quo=
t;<br>
<br>
=A0 =A0 =A0 =A0 prime_factors &lt;&lt; divisor<br>
<br>
=A0 =A0 =A0 =A0 puts &quot;Factors array now set: #{prime_factors.inspect}&=
quot;<br>
<br>
=A0 =A0 =A0 =A0 quotient =3D factor / divisor<br>
<br>
=A0 =A0 =A0 =A0 factor =3D quotient<br>
<br>
=A0 =A0 =A0 end #/if loop<br>
<br>
=A0 end #/do<br>
=A0 puts<br>
=A0 puts &quot;Exiting loop; #{factor} is the last quotient to&#39;ve passe=
d if<br>
statement.&quot;<br>
=A0 prime_factors &lt;&lt; factor<br>
=A0 p prime_factors<br>
end<br>
<br>
# primes(256) # should print [2,2,2,2,2,2,2,2]<br>
# primes(100) # should print [2,2,5,5]<br>
# primes(81) # should print [3,3,3,3]<br>
# primes(10) # should print [2,5]<br>
primes(8) # should print [2,2,2] --&gt; currently prints [2,4]<br>
<span class=3D"HOEnZb"><font color=3D"#888888"><br>
--<br>
Posted via <a href=3D"http://www.ruby-forum.com/" target=3D"_blank">http://=
www.ruby-forum.com/</a>.<br>
<br>
</font></span></blockquote></div><br><br clear=3D"all"><div><br></div>-- <b=
r>David N. Springer<br>Eau Claire, WI<br>
</div>

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