# Problem

Say you have an array for which the ith element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.

Example 1:

``````Input: [7, 1, 5, 3, 6, 4]
Output: 5

max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)
``````

Example 2:

``````Input: [7, 6, 4, 3, 1]
Output: 0

In this case, no transaction is done, i.e. max profit = 0.
``````

# Python 实现

``````
'''
Say you have an array for which the ith element is the price of a given stock on day i.

If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock),
design an algorithm to find the maximum profit.

Example 1:
Input: [7, 1, 5, 3, 6, 4]
Output: 5

max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)
Example 2:
Input: [7, 6, 4, 3, 1]
Output: 0

In this case, no transaction is done, i.e. max profit = 0.
'''

#author li.hzh

class Solution:
def maxProfit(self, prices):
"""
:type prices: List[int]
:rtype: int
"""
if prices is None or len(prices) <= 1:
return 0
min_val = prices
profit = 0
for index in range(1, len(prices)):
cur_val = prices[index]
if cur_val < min_val:
min_val = cur_val
cur_profit = cur_val - min_val
if cur_profit > profit:
profit = cur_profit
return profit

print(Solution().maxProfit([7, 1, 5, 3, 6, 4]))
print(Solution().maxProfit([7, 6, 4, 3, 1]))
print(Solution().maxProfit([7, 6, 7, 3, 5]))

``````

Thanks a lot.