Write a method mode which takes an Array of numbers
as its input and returns an Array of the most frequent values.

If there's only one most-frequent value, it returns a
 single-element Array.

For example,

mode([1,2,3,3])         # => [3]
mode([4.5, 0, 0])       # => [0]
mode([1.5, -1, 1, 1.5]) # => [1.5]
mode([1,1,2,2])         # => [1,2]
mode([1,2,3])           # => [1,2,3], because all occur with
                                      equal frequency


def mode(array)
  f = Hash.new(0)

  array.each do |x|
    f[x] += 1
  end

  max = 0
  modes = []
  f.each do |key, value|
    if value > max
      modes = [key]
      max = value
    elsif value == max
      modes.push(key)
    end
  end

  modes
end