10min，最大连续子序列和
class Solution:
def maxProfit(self, prices: List[int]) -> int:
min_,max_=100000000,0 # 这里赋值为0而不能-1，是因为特殊情况
for i in range(0,len(prices)): #这里不能从1开始
min_=min(min_,prices[i])
if prices[i]>min_:
max_=max(max_,prices[i]-min_)
return max_
15min，状态机
初始化的时候注意-无穷和0，max 取-
https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-iii/solution/yi-ge-tong-yong-fang-fa-tuan-mie-6-dao-gu-piao-wen/
class Solution2:
def maxProfit(self, prices: List[int]) -> int:
if not prices:return 0
dpi0,dpi1=0,-prices[0]
for i in range(1,len(prices)):
dpi0=max(dpi0,dpi1+prices[i])
dpi1=max(dpi1,-prices[i])
return dpi0
