You are given coins of different denominations and a total amount of money. Write a function to compute the number of combinations that make up that amount. You may assume that you have infinite number of each kind of coin.
You can assume that
0 <= amount <= 5000
1 <= coin <= 5000
the number of coins is less than 500
the answer is guaranteed to fit into signed 32-bit integer
Input: amount = 5, coins = [1, 2, 5]
Explanation: there are four ways to make up the amount:
Input: amount = 3, coins = 
Explanation: the amount of 3 cannot be made up just with coins of 2.