零钱兑换 II

/*
 * Problem Statement: Given an array of integers coins representing different denominations and an integer amount representing a total amount of money, return the number of combinations that make up that amount. If that amount cannot be reached, return 0. The problem guarantees that the result fits in a 32-bit signed integer.
 * 
 * Approach: This solution also uses dynamic programming but leverages Java Streams for some operations. We create a dp array similar to the previous solution, but this time we use streams to manipulate the data.
 */
 
import java.util.Arrays;
import java.util.stream.IntStream;
 
public class CoinChange2 {
    public int change(int amount, int[] coins) {
        int[] dp = new int[amount + 1];
        dp[0] = 1; // Base case: one way to make amount 0
 
        Arrays.stream(coins).forEach(coin -> 
            IntStream.range(coin, amount + 1).forEach(i -> dp[i] += dp[i - coin])
        );
        return dp[amount];
    }
}