All factors of a given number

by

In Ruby, the prime library gives you the factorization:

require 'prime'
4800.prime_division #=> [[2, 6], [3, 1], [5, 2]]

To get that list of yours, you take the cartesian product of the possible powers:

require 'prime'
def factors_of(number)
  primes, powers = number.prime_division.transpose
  exponents = powers.map{|i| (0..i).to_a}
  divisors = exponents.shift.product(*exponents).map do |powers|
    primes.zip(powers).map{|prime, power| prime ** power}.inject(:*)
  end
  divisors.sort.map{|div| [div, number / div]}
end

p factors_of(4800) # => [[1, 4800], [2, 2400], ..., [4800, 1]]

Note: In Ruby 1.8.7, you must require 'mathn' instead of require 'prime'. In Ruby 1.8.6, require 'backports/1.8.7/enumerable/inject' or modify the inject above…

More Related Contents:

  1. Very Basic Ruby puts and gets
  2. Why is division in Ruby returning an integer instead of decimal value?
  3. How to sum array of numbers in Ruby?
  4. What’s the best way to model recurring events in a calendar application? [closed]
  5. Learning Insertion Sort in Ruby
  6. Sort an array according to the elements of another array
  7. Ruby factorial function
  8. Round up to the nearest tenth?
  9. How to determine if a point is in a 2D triangle? [closed]
  10. Ruby: String Comparison Issues
  11. Writing your own square root function
  12. Creating all possible k combinations of n items in C++
  13. Why is `a = a` `nil` in Ruby?
  14. Print two-dimensional array in spiral order
  15. What exactly is `&:capitalize` in Ruby?
  16. Ruby’s File.open and the need for f.close
  17. Difference between map and collect in Ruby?
  18. How to check whether a string contains a substring in Ruby
  19. How to find the smallest number with just 0 and 1 which is divided by a given number?
  20. Fastest algorithm for primality test [closed]
  21. Is there an efficient algorithm for integer partitioning with restricted number of parts?
  22. How to get a specific output iterating a hash in Ruby?
  23. Does Ruby perform Tail Call Optimization?
  24. How do I use define_method to create class methods?
  25. When to use each method of launching a subprocess in Ruby
  26. Ruby run shell command in a specific directory
  27. Check if URL exists in Ruby
  28. Using Ruby Symbols
  29. How to use double brackets in a regular expression?
  30. Is there a ‘variable_get’ method? If not, how can I create my own?

Leave a Comment