String Compression: Implement a method to perform basic string compression using the counts of repeated characters. For example, the string aabcccccaaa would become a2blc5a3. If the "compressed" string would not become smaller than the original string, your method should return the original string. You can assume the string has only uppercase an…

compressed_string.py

"""
String Compression: Implement a method to perform basic string 
compression using the counts of repeated characters. For example, 
the string aabcccccaaa would become a2blc5a3. If the "compressed" 
string would not become smaller than the original string, your 
method should return the original string. You can assume the 
string has only uppercase and lowercase letters (a -z). 
"""
def compress(inputstr):
    if len(inputstr) == 0:
        return ""

    prev = inputstr[0]
    count = 0
    compressed = []
    for c in inputstr:

        if prev == c:
            count += 1
        else:
            compressed.append(prev)
            compressed.append(str(count))
            count = 1
        prev = c

    compressed.append(prev)
    compressed.append(str(count))
    output = "".join(compressed)
    if len(output) > len(inputstr):
        return inputstr
    else:
        return output

import unittest
class TestCompress(unittest.TestCase):

    def test_sample_case(self):
        self.assertEqual(compress("aabcccccaaa"), "a2b1c5a3")

    def test_empty(self):
        self.assertEqual(compress(""), "")

    def test_one(self):
        self.assertEqual(compress("a"), "a")

    def test_no_compression(self):
        self.assertEqual(compress("abcdefghijklmnop"), "abcdefghijklmnop")

    def test_front_compress(self):
        self.assertEqual(compress("aaaaabc"), "a5b1c1")

    def test_mid_compress(self):
        self.assertEqual(compress("abbbbbbbbc"), "a1b8c1")

    def test_end_compress(self):
        self.assertEqual(compress("abccccc"), "a1b1c5")

    def test_equal_length(self):
        self.assertEqual(compress("aabb"), "a2b2")

    def test_output_is_longer(self):
        self.assertEqual(compress("aabcdefghijklmnop"), "aabcdefghijklmnop")


if __name__ == '__main__':
    unittest.main()

Before arriving to this solution, it was coded and tested using pencil and paper first.