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Your quirky boss collects rare, old coins...

They found out you're a programmer and asked you to solve something they've been wondering for a long time.

Write a function that, given:

  1. an amount of money
  2. an array of coin denominations

computes the number of ways to make the amount of money with coins of the available denominations.

Example: for amount=4 (4¢) and denominations=[1,2,3] (1¢, 2¢ and 3¢), your program would output 4—the number of ways to make 4¢ with those denominations:

  1. 1¢, 1¢, 1¢, 1¢
  2. 1¢, 1¢, 2¢
  3. 1¢, 3¢
  4. 2¢, 2¢

What if there's no way to make the amount with the denominations? Does your function have reasonable behavior?

We can do this in time and space, where n is the amount of money and m is the number of denominations.

A simple recursive approach works, but you'll find that your function gets called more than once with the same inputs. We can do better.

We could avoid the duplicate function calls by memoizing, but there's a cleaner bottom-up approach.

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Start your free trial!

Log in or sign up with one click to get immediate access to free mock interview questions

Where do I enter my password?

Actually, we don't support password-based login. Never have. Just the OAuth methods above. Why?

  1. It's easy and quick. No "reset password" flow. No password to forget.
  2. It lets us avoid storing passwords that hackers could access and use to try to log into our users' email or bank accounts.
  3. It makes it harder for one person to share a paid Interview Cake account with multiple people.

time and additional space, where n is the amount of money and m is the number of potential denominations.

Start your free trial!

Log in or sign up with one click to get immediate access to free mock interview questions

Where do I enter my password?

Actually, we don't support password-based login. Never have. Just the OAuth methods above. Why?

  1. It's easy and quick. No "reset password" flow. No password to forget.
  2. It lets us avoid storing passwords that hackers could access and use to try to log into our users' email or bank accounts.
  3. It makes it harder for one person to share a paid Interview Cake account with multiple people.

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