经典动态规划

def count_ways(coins, m):
    dp = [0 for i in range(m + 1)]
    dp[0] = 1
    for coin in coins:
        for i in range(coin, m + 1):
            dp[i] += dp[i - coin]
    return dp[m]
n, m = map(int, input().split())
coins = [int(input()) for i in range(n)]
ways = count_ways(coins, m)
print(ways)

动态规划是正向计算的，我们不妨先试试逆向理解 或者按照代码推演一遍