miguel soln to string compression 1.6

Author: miguelHx

Python/chapter01/1.6 - String Compression/miguel_1.6_sol.py

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+"""
+Python version 3.7.0
+1.6 - String Compression
+Implement a method to perform basic string compression using the counts
+of repeated characters. For example, the string aabcccccaaa would become a2b1c5a3.
+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).
+"""
+import unittest
+from typing import Callable
+
+
+def str_compression(s: str) -> str:
+    """
+    String compression will attempt to reduce the size of s by condensing
+    s using the counts of repeated characters.
+    Runtime: O(n), asymptotic runtime depends on size of s
+    Space Complexity: O(n), compressed list
+    :param s: the string we want to compress
+    :return: the compressed string or s if the compressed string is not smaller
+    """
+    if len(s) == 0:
+        return s
+    compressed = []
+    prev_char = s[0]
+    count = 1
+    for c in s[1:len(s)]:
+        if c == prev_char:
+            count += 1
+            continue
+        compressed.append(prev_char)
+        compressed.append(str(count)[0])
+        prev_char = c
+        count = 1
+    # clean up: last character count
+    compressed.append(prev_char)
+    compressed.append(str(count)[0])
+
+    return ''.join(compressed) if len(compressed) < len(s) else s
+
+
+class TestStringCompressionFunction(unittest.TestCase):
+    def _run_tests(self, f: Callable[[str], str]) -> None:
+        cases = [
+            ('aabcccccaaa', 'a2b1c5a3'),
+            ('abcde', 'abcde'),
+            ('aabbccdd', 'aabbccdd'),
+            ('', ''),
+            ('c', 'c'),
+            ('aaAAccCCCCC', 'a2A2c2C5')
+        ]
+        for s, expected in cases:
+            self.assertEqual(f(s), expected, msg=(s, expected))
+
+    def test_string_compression(self):
+        self._run_tests(str_compression)
+
+
+if __name__ == '__main__':
+    unittest.main()