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

Challenge Notebook

Problem: Swap the odd and even bits of a positive integer with as few operations as possible.

Constraints

  • Can we assume the input is always a positive int?
    • Yes
  • Can we assume we're working with 32 bits?
    • Yes
  • Is the output an int?
    • Yes
  • Can we assume the inputs are valid (not None)?
    • No
  • Can we assume this fits memory?
    • Yes

Test Cases

  • None -> Exception
  • 0 -> 0
  • -1 -> -1
  • General case
      input  = 1001 1111 0110
      result = 0110 1111 1001

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 pairwise_swap(self, num):
        # TODO: Implement me
        pass

Unit Test

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

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


class TestBits(unittest.TestCase):

    def test_pairwise_swap(self):
        bits = Bits()
        self.assertEqual(bits.pairwise_swap(0), 0)
        self.assertEqual(bits.pairwise_swap(1), 1)
        num = int('0000100111110110', base=2)
        expected = int('0000011011111001', base=2)
        self.assertEqual(bits.pairwise_swap(num), expected)
        print('Success: test_pairwise_swap')


def main():
    test = TestBits()
    test.test_pairwise_swap()


if __name__ == '__main__':
    main()

Solution Notebook

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