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

Challenge Notebook

Problem: Given a positive integer, get the next largest number and the next smallest number with the same number of 1's as the given number.

Constraints

  • Is the output a positive int?
    • Yes
  • Can we assume the inputs are valid?
    • No
  • Can we assume this fits memory?
    • Yes

Test Cases

  • None -> Exception
  • 0 -> Exception
  • negative int -> Exception
  • General case:
      * Input:         0000 0000 1101 0111
      * Next largest:  0000 0000 1101 1011
      * Next smallest: 0000 0000 1100 1111
    

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 Bits(object):

    def get_next_largest(self, num):
        # TODO: Implement me
        pass

    def get_next_smallest(self, num):
        # TODO: Implement me
        pass

Unit Test

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

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


class TestBits(unittest.TestCase):

    def test_get_next_largest(self):
        bits = Bits()
        self.assertRaises(Exception, bits.get_next_largest, None)
        self.assertRaises(Exception, bits.get_next_largest, 0)
        self.assertRaises(Exception, bits.get_next_largest, -1)
        num = int('011010111', base=2)
        expected = int('011011011', base=2)
        self.assertEqual(bits.get_next_largest(num), expected)
        print('Success: test_get_next_largest')

    def test_get_next_smallest(self):
        bits = Bits()
        self.assertRaises(Exception, bits.get_next_smallest, None)
        self.assertRaises(Exception, bits.get_next_smallest, 0)
        self.assertRaises(Exception, bits.get_next_smallest, -1)
        num = int('011010111', base=2)
        expected = int('011001111', base=2)
        self.assertEqual(bits.get_next_smallest(num), expected)
        print('Success: test_get_next_smallest')

def main():
    test = TestBits()
    test.test_get_next_largest()
    test.test_get_next_smallest()


if __name__ == '__main__':
    main()

Solution Notebook

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