From https://www.schmengler-se.de/en/2017/02/tdd-kata-07-coin-changer/ :
You've just created a virtual vending machine that will dispense widgets of programming goodness when a user puts money into the machine. The machine should dispense the proper change. You now need the programming logic to determine which coins to dispense.
Write a program that will correctly determine the least number of coins to be given to the user such that the sum of the coins' value would equal the correct amount of change.
Input: change amount Input: coin denomination array (ie [1, 5, 10, 25, 100] ) Output: number of coins array (ie [1, 0, 1, 0, 0] would represent $0.11
For example An input of 15 with [1, 5, 10, 25, 100] should return fifteen cents or [0, 1, 1, 0, 0] An input of 40 with [1, 5, 10, 25, 100] should return two dimes or [0, 1, 1, 1, 0]
Part of the challenge with this exercise is to think through your testing strategy. Do you test every possible input for the change amount, or do you test specific boundary cases?
Use Test Driven Development (TDD) to solve this problem. Start writing tests, write enough code to get the tests to pass, and then refactor your code. Allow your design to emerge from writing tests; don't try to solve the problem first.
If you prefer to return a hash instead of am array, that's ok too. {1 => 1, 5 => 0, 10 => 1, 25 => 0, 100 => 0} equals $0.11
This solution doesn't calculate the least amount of coins yet. Consider the case where the change should be 30 and the available coins are [1, 10, 25]. The optimal output is [0, 3, 0], which is 3 coins. Ours outputs [5, 0, 1], which is 6 coins.
Abraão L. N. Lourenço, abraao@alourenco.com, https://github.com/abraao
Xavi Medina Torregrosa, xavimeditor@gmail.com, https://github.com/XaviMedina