How should I practice Coin Change II?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Bloomberg LP phone screen and onsite interview problems in FastPrep.

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Coin Change II

Bloomberg LP● MediumNEW GRADPHONE SCREENONSITE INTERVIEW

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Problem statement

Given distinct positive denominations coins and a nonnegative amount, return the number of unordered combinations that sum exactly to amount.

You may use each denomination any number of times. Different orders of the same multiset count once.

Function

countCoinChangeCombinations(coins: int[], amount: int) → long

Examples

Example 1

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

The combinations are 5; 2+2+1; 2+1+1+1; and five 1s.

Example 2

coins = [2]amount = 3return = 0

No number of 2s sums to 3.

Constraints

1 <= coins.length <= 100.
1 <= coins[i] <= 5000 and denominations are distinct.
0 <= amount <= 5000.
The answer fits in a signed 64-bit integer.