动态追踪当前最小值，当前最大利润和全局利润对比
class Solution:
def largestprofit(self,A):
if len(A) < 2:
return 0
min = A[0]
res = max(A[1] - A[0],0)
for i in range(2,len(A)):
if A[i-1] < min:
min = A[i-1]
current = A[i] - min
res = max(current,res)
return res
S = Solution()
print(S.largestprofit([9,11,8,5,7,12,16,14]))
