d4d8397e5f
Adds some of the code I generated while studying for a role transfer at Google using the fantastic resource, InterviewCake.com. This work predates the mono-repo. I should think of ways to DRY up this code and the code in crack_the_coding_interview, but I'm afraid I'm creating unnecessary work for myself that way.
89 lines
2.5 KiB
Python
89 lines
2.5 KiB
Python
import unittest
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################################################################################
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# Solution
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################################################################################
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# f :: [Int] -> Int
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def highest_product_of_3(xs):
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"""Here we're greedily storing:
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- current max
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- largest product of two
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- largest positive number
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- second largest positive number
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- largest negative number
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"""
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if len(xs) < 3:
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raise Exception
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cm = None
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ld = xs[0] * xs[1]
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l2 = min(xs[0], xs[1])
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if xs[0] < 0 or xs[1] < 0:
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ln = min(xs[0], xs[1])
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else:
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ln = 1
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l = max(xs[0], xs[1])
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for x in xs[2:]:
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if not cm:
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cm = max(x * ln * l, ld * x, x * l * l2) # beware
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ld = max(ld, x * ln, x * l)
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ln = min(ln, x)
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l = max(l, x)
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if x < l:
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l2 = max(l2, x)
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else:
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cm = max(cm, x * ln * l, x * ld, x * l * l2)
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ld = max(ld, x * ln, x * l)
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ln = min(ln, x)
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l = max(l, x)
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if x < l:
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l2 = max(l2, x)
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return cm
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################################################################################
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# Tests
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################################################################################
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class Test(unittest.TestCase):
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def test_short_list(self):
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actual = highest_product_of_3([1, 2, 3, 4])
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expected = 24
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self.assertEqual(actual, expected)
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def test_longer_list(self):
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actual = highest_product_of_3([6, 1, 3, 5, 7, 8, 2])
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expected = 336
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self.assertEqual(actual, expected)
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def test_list_has_one_negative(self):
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actual = highest_product_of_3([-5, 4, 8, 2, 3])
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expected = 96
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self.assertEqual(actual, expected)
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def test_list_has_two_negatives(self):
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actual = highest_product_of_3([-10, 1, 3, 2, -10])
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expected = 300
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self.assertEqual(actual, expected)
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def test_list_is_all_negatives(self):
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actual = highest_product_of_3([-5, -1, -3, -2])
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expected = -6
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self.assertEqual(actual, expected)
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def test_error_with_empty_list(self):
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with self.assertRaises(Exception):
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highest_product_of_3([])
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def test_error_with_one_number(self):
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with self.assertRaises(Exception):
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highest_product_of_3([1])
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def test_error_with_two_numbers(self):
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with self.assertRaises(Exception):
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highest_product_of_3([1, 1])
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unittest.main(verbosity=2)
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