This notebook was prepared by Donne Martin. Source and license info is on GitHub.

Challenge Notebook

Problem: Find the highest product of three numbers in a list.

Constraints

  • Is the input a list of integers?
    • Yes
  • Can we get negative inputs?
    • Yes
  • Can there be duplicate entries in the input?
    • Yes
  • Will there always be at least three integers?
    • No
  • Can we assume the inputs are valid?
    • No, check for None input
  • Can we assume this fits memory?
    • Yes

Test Cases

  • None -> TypeError
  • Less than three ints -> ValueError
  • [5, -2, 3] -> -30
  • [5, -2, 3, 1, -1, 4] -> 60

Algorithm

Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.

Code

In [ ]:
class Solution(object):

    def max_prod_three(self, array):
        # TODO: Implement me
        pass

Unit Test

The following unit test is expected to fail until you solve the challenge.

In [ ]:
# %load test_prod_three.py
import unittest


class TestProdThree(unittest.TestCase):

    def test_prod_three(self):
        solution = Solution()
        self.assertRaises(TypeError, solution.max_prod_three, None)
        self.assertRaises(ValueError, solution.max_prod_three, [1, 2])
        self.assertEqual(solution.max_prod_three([5, -2, 3]), -30)
        self.assertEqual(solution.max_prod_three([5, -2, 3, 1, -1, 4]), 60)
        print('Success: test_prod_three')


def main():
    test = TestProdThree()
    test.test_prod_three()


if __name__ == '__main__':
    main()

Solution Notebook

Review the Solution Notebook for a discussion on algorithms and code solutions.