ChangeMachine.rb

=begin

Implement a change function that performs at O(n) (we will test for this).

The function will accept an integer parameter that represents cents, and returns
the optimal change using the least number of coins.

The function should return a hash containing a key for each coin of US currency
(specifically 25¢ 10¢ 5¢ and 1¢ coins -- don't use 50¢ or 100¢ coins). The value
of each coin should represent the count of each coin in the change.

The function should return a hash with all coin count values set to 0 if the
cents parameter is less than or equal to 0.

change(31)
# => { 25 => 1, 10 => 0, 5 => 1, 1 => 1 }

=end

# My Solution
def change(cents)
  return { 25 => 0, 10 => 0, 5 => 0, 1 => 0 } if cents < 0
  change = {}
  change[25] = (cents/25)
  cents = cents % 25
  change[10] = (cents/10)
  cents = cents % 10
  change[5] = (cents/5)
  cents = cents % 5
  change[1] = (cents/1)
  cents = cents % 1
  change
end

# Better Solution
def change(cents)
  [25, 10, 5, 1].map.with_object({}) { |c, h|
    h[c] = cents > 0 ? cents / c : 0
    cents -= h[c] * c
  }
end

# Another Solution
def change(cents)
  change = { 25 => 0, 10 => 0, 5 => 0, 1 => 0 }
  cents <= 0 ? change : change.each_key { |c| change[c] = cents / c; cents = cents % c }
end