Tracks
/
Python
Python
/
Exercises
/
Change
Change

Change

Medium
OverviewCommunity Solutions

Introduction

In the mystical village of Coinholt, you stand behind the counter of your bakery, arranging a fresh batch of pastries. The door creaks open, and in walks Denara, a skilled merchant with a keen eye for quality goods. After a quick meal, she slides a shimmering coin across the counter, representing a value of 100 units.

You smile, taking the coin, and glance at the total cost of the meal: 88 units. That means you need to return 12 units in change.

Denara holds out her hand expectantly. "Just give me the fewest coins," she says with a smile. "My pouch is already full, and I don't want to risk losing them on the road."

You know you have a few options. "We have Lumis (worth 10 units), Viras (worth 5 units), and Zenth (worth 2 units) available for change."

You quickly calculate the possibilities in your head:

  • one Lumis (1 × 10 units) + one Zenth (1 × 2 units) = 2 coins total
  • two Viras (2 × 5 units) + one Zenth (1 × 2 units) = 3 coins total
  • six Zenth (6 × 2 units) = 6 coins total

"The best choice is two coins: one Lumis and one Zenth," you say, handing her the change.

Denara smiles, clearly impressed. "As always, you've got it right."

Instructions

Determine the fewest number of coins to give a customer so that the sum of their values equals the correct amount of change.

Examples

  • An amount of 15 with available coin values [1, 5, 10, 25, 100] should return one coin of value 5 and one coin of value 10, or [5, 10].
  • An amount of 40 with available coin values [1, 5, 10, 25, 100] should return one coin of value 5, one coin of value 10, and one coin of value 25, or [5, 10, 25].

Exception messages

Sometimes it is necessary to raise an exception. When you do this, you should always include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. For situations where you know that the error source will be a certain type, you can choose to raise one of the built in error types, but should still include a meaningful message.

This particular exercise requires that you use the raise statement to "throw" a ValueError when change cannot be made with the coins given. The tests will only pass if you both raise the exception and include a message with it.

To raise a ValueError with a message, write the message as an argument to the exception type:

# example when change cannot be made with the coins passed in
raise ValueError("can't make target with given coins")

Source

Software Craftsmanship - Coin Change KataThe link opens in a new window or tab
Edit via GitHub The link opens in a new window or tab
Python Exercism

Ready to start Change?

Sign up to Exercism to learn and master Python with 17 concepts, 140 exercises, and real human mentoring, all for free.

Sign up, it’s free! Log in to Exercism