This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).

Challenge Notebook

Problem: Implement an algorithm to determine if a string has all unique characters

Constraints
Test Cases
Algorithm
Code
Unit Test
Solution Notebook

Constraints

Can you assume the string is ASCII?
- Yes
- Note: Unicode strings could require special handling depending on your language
Can we assume this is case sensitive?
- Yes
Can you use additional data structures?
- Yes

Test Cases

'' -> True
'foo' -> False
'bar' -> True

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 [ ]:

    
def unique_chars(string):
    # TODO: Implement me
    pass

Unit Test

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



In [ ]:

    
# %load test_unique_chars.py
from nose.tools import assert_equal


class TestUniqueChars(object):

    def test_unique_chars(self, func):
        assert_equal(func(''), True)
        assert_equal(func('foo'), False)
        assert_equal(func('bar'), True)
        print('Success: test_unique_chars')


def main():
    test = TestUniqueChars()
    test.test_unique_chars(unique_chars)
    try:
        test.test_unique_chars(unique_chars_hash)
        test.test_unique_chars(unique_chars_inplace)
    except NameError:
        # Alternate solutions are only defined
        # in the solutions file
        pass


if __name__ == '__main__':
    main()

Solution Notebook

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