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def get_max_profit(xs):
best_profit = xs[1] - xs[0]
lowest_buy = xs[0]
for x in xs[1:]:
best_profit = max(best_profit, x - lowest_buy)
lowest_buy = min(lowest_buy, x)
return best_profit
# Tests
import unittest
class Test(unittest.TestCase):
def test_price_goes_up_then_down(self):
actual = get_max_profit([1, 5, 3, 2])
expected = 4
self.assertEqual(actual, expected)
def test_price_goes_down_then_up(self):
actual = get_max_profit([7, 2, 8, 9])
expected = 7
self.assertEqual(actual, expected)
def test_price_goes_up_all_day(self):
actual = get_max_profit([1, 6, 7, 9])
expected = 8
self.assertEqual(actual, expected)
def test_price_goes_down_all_day(self):
actual = get_max_profit([9, 7, 4, 1])
expected = -2
self.assertEqual(actual, expected)
def test_price_stays_the_same_all_day(self):
actual = get_max_profit([1, 1, 1, 1])
expected = 0
self.assertEqual(actual, expected)
def test_error_with_empty_prices(self):
with self.assertRaises(Exception):
get_max_profit([])
def test_error_with_one_price(self):
with self.assertRaises(Exception):
get_max_profit([1])
unittest.main(verbosity=2)
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