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

- Is the input an int, base 2?
- Yes

- Can we assume the input is a 32 bit number?
- Yes

- Do we have to validate the length of the input?
- No

- Is the output an int?
- Yes

- Can we assume the inputs are valid?
- No

- Can we assume we are using a positive number since Python doesn't have an >>> operator?
- Yes

- Can we assume this fits memory?
- Yes

- None -> Exception
- All 1's -> Count of 1s
- All 0's -> 1
- General case
- 0000 1111 1101 1101 1111 0011 1111 0000 -> 10 (ten)

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.

In [ ]:

```
class Bits(object):
def flip_bit(self, num):
# TODO: Implement me
pass
```

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

In [ ]:

```
# %load test_flip_bit.py
import unittest
class TestBits(unittest.TestCase):
def test_flip_bit(self):
bits = Bits()
self.assertRaises(TypeError, bits.flip_bit, None)
self.assertEqual(bits.flip_bit(0), 1)
self.assertEqual(bits.flip_bit(-1), bits.MAX_BITS)
num = int('00001111110111011110001111110000', base=2)
expected = 10
self.assertEqual(bits.flip_bit(num), expected)
num = int('00000100111011101111100011111011', base=2)
expected = 9
self.assertEqual(bits.flip_bit(num), expected)
num = int('00010011101110111110001111101111', base=2)
expected = 10
self.assertEqual(bits.flip_bit(num), expected)
print('Success: test_print_binary')
def main():
test = TestBits()
test.test_flip_bit()
if __name__ == '__main__':
main()
```

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