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

Challenge Notebook¶

Problem: Find the length of the longest substring with at most k distinct characters.¶

Constraints
Test Cases
Algorithm
Code
Unit Test
Solution Notebook

Constraints¶

Can we assume the inputs are valid?
- No
Can we assume the strings are ASCII?
- Yes
Is this case sensitive?
- Yes
Is a substring a contiguous block of chars?
- Yes
Do we expect an int as a result?
- Yes
Can we assume this fits memory?
- Yes

Test Cases¶

None -> TypeError
'', k = 3 -> 0
'abcabcdefgghiij', k=3 -> 6
'abcabcdefgghighij', k=3 -> 7

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 longest_substr(self, string, k):
        # TODO: Implement me
        pass

Unit Test¶

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

In [ ]:

# %load test_longest_substr.py
import unittest


class TestSolution(unittest.TestCase):

    def test_longest_substr(self):
        solution = Solution()
        self.assertRaises(TypeError, solution.longest_substr, None)
        self.assertEqual(solution.longest_substr('', k=3), 0)
        self.assertEqual(solution.longest_substr('abcabcdefgghiij', k=3), 6)
        self.assertEqual(solution.longest_substr('abcabcdefgghighij', k=3), 7)
        print('Success: test_longest_substr')


def main():
    test = TestSolution()
    test.test_longest_substr()


if __name__ == '__main__':
    main()

Solution Notebook¶

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