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121. Best Time to Buy and Sell Stock.py
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121. Best Time to Buy and Sell Stock.py
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import unittest
# 121. Best Time to Buy and Sell Stock
#
# 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 (i.e., buy one and sell
# one share of the stock), design an algorithm to find the maximum profit.
# Note that you cannot sell a stock before you buy one.
#
# Example 1:
#
# Input: [7,1,5,3,6,4]
# Output: 5
# Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
# Not 7-1 = 6, as selling price needs to be larger than buying price.
class unitest(unittest.TestCase):
def testEmptyList(self):
input = []
output = 0
self.assertEqual(Solution().maxProfit(input), output)
def test_a(self):
input = [7,1,5,3,6,4]
output = 5
self.assertEqual(Solution().maxProfit(input), output)
class Solution(object):
def maxProfit(self, prices):
"""
:type prices: List[int]
:rtype: int
"""
if not prices:
return 0
min_price = prices[0]
max_profit = 0
for n in prices:
if n < min_price:
min_price = n
elif max_profit < n - min_price:
max_profit = n - min_price
return max_profit
if __name__ == '__main__':
unittest.main()