How should I practice Coin Change II?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Apple phone screen problems in FastPrep.

Is Coin Change II associated with Apple?

FastPrep tags this as a Apple phone screen coding practice problem when the problem catalog has that company and stage context.

Coin Change II

Apple● MediumFULLTIMEPHONE SCREEN

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Problem statement

You have an unlimited supply of each distinct denomination in coins. Count the combinations that sum to amount.

Order does not distinguish combinations: using coins 1,2,2 is the same combination as using 2,1,2. Return 0 when no combination exists. Amount 0 has one combination, the empty selection.

The requested count fits in a signed 32-bit integer.

Function

change(amount: int, coins: int[]) → int

Examples

Example 1

amount = 5coins = [1,2,5]return = 4

The combinations are [5], [2,2,1], [2,1,1,1], and [1,1,1,1,1].

Example 2

amount = 3coins = [2]return = 0

No combination of denomination 2 reaches an odd amount.

Example 3

amount = 10coins = [10]return = 1

Only one coin of denomination 10 is needed.

Constraints

1 <= coins.length <= 300.
All denominations are distinct, with 1 <= coins[i] <= 5000.
0 <= amount <= 5000.
The answer is at most 2^31 - 1.