nimamehanian

class Integer
  def prime?
    if self.even? && self != 2 ||
      self.send(:sum_of_digits_div_by_three?) && self != 3 ||
        self.send(:last_two_digits_div_by_four?) ||
          self.send(:last_digit_div_by_five?) && self != 5
      return false
    else
      return true
    end

nimamehanian

def countem(list_of_lists)
  occurrences = {}
  list_of_lists.each do |inner_list|
    inner_list.each_with_index do |integer, index_of_integer|
      if occurrences.has_key?("#{integer} @ #{index_of_integer}") == false
        # if not there, add it
        occurrences["#{integer} @ #{index_of_integer}"] = 1
      else
        # if there, increment
        occurrences["#{integer} @ #{index_of_integer}"] += 1

nimamehanian

class Array
  def mixup
    length = self.length
    while length > 0
      length -= 1
      break if length == 0
      randomIndex = (rand * (length - 1)).floor
      self[length], self[randomIndex] = self[randomIndex], self[length]
    end
  end

nimamehanian

class Array
  def backwards
    length = self.length
    i = 1
    while i != length
      i += 1
      value = self.slice!(length - i)
      self << value
      break if self[length - i] == self[0]
    end

nimamehanian

def anagrams?(word_one, word_two)
  word_one = word_one.split('').sort
  word_two = word_two.split('').sort

  word_one == word_two ? true : false
end

nimamehanian

class Rpn
  def evaluate(expression)
    operators = ['+', '-', '*']
    stack = []
    symbols = expression.split(' ')

    symbols.each do |symbol|
      if operators.include?(symbol) 
        number_two = stack.pop
        number_one = stack.pop