class Solution(object):
def coinChange(self, coins, amount):
"""
:type coins: List[int]
:type amount: int
:rtype: int
"""
if amount == 0: return 0
coins.sort()
if coins[0] > amount: return -1
dp = [0] + [float('inf')] * amount # dp[i]: 硬币能组成金额为i所需最小个数
for coin in coins: # 每次新拿一种硬币
for i in range(coin, amount + 1): # 从大于等于这个硬币的面值开始，这个硬币才可能开始起作用
dp[i] = min(dp[i], dp[i - coin] + 1)
return dp[-1] if dp[-1] != float('inf') else -1
