Merge pull request #36 from miguelHx/miguel_1.9_string_rotation

Miguel 1.9 - String Rotation [Python]

Author: lhchavez

Python/chapter01/1.9 - String Rotation/miguel_1.9_sol.py

@@ -0,0 +1,83 @@
+"""
+Python version 3.7.0
+1.9 - String Rotation
+Assume you have a method isSubstring which
+checks if one word is a substring
+of another.  Given two strings, s1 and s2,
+write code to check if s2 is a
+rotation of s1 using only one call to isSubstring
+(e.g. 'waterbottle' is a rotation of 'erbottlewat')
+"""
+import unittest
+
+
+def is_substring(sub: str, s: str) -> bool:
+    """
+    is_substring checks if 'sub' is a substring of 's'
+    :param sub: the substring
+    :param s: the alleged full string
+    :return: true if sub is a substring of s, false otherwise
+    """
+    return sub in s
+
+
+def string_rotation(s1: str, s2: str) -> bool:
+    """
+    Given two strings, string_rotation will check if s2 is a rotation of s1
+    using only one call to isSubstring.
+    Assume s2 is a rotation of s1.  s1 is a rearrangement of s2.
+    Choosing an index where we rotate to be any index,
+    let s1 and s2 consist of two parts, a and b.
+    The original string will be s2 = ab.
+    The rotated string will be s1 = ba.
+    Since we are using substring, we want s2 = ab to appear in
+    a larger string ..ab..
+    This is guaranteed to happen if we have s1 + s1 = baba
+    because ab shows up in there.
+    Runtime: worst case: O(n^2) - substring found at end of full string
+    Space Complexity:  O(n)
+    :param s1: the rotated string
+    :param s2: the original string
+    :return: true if s2 is a rotation of s1, false otherwise
+    """
+    # not rotation if lengths don't match
+    if len(s1) != len(s2):
+        return False
+    return is_substring(s2, s1 + s1)
+
+
+class TestStringRotation(unittest.TestCase):
+
+    def setUp(self):
+        self.str_rotation_cases = [
+            ('erbottlewat', 'waterbottle', True),
+            ('erbottlewet', 'weterbottle', True),
+            ('same', 'same', True),
+            ('oneoff', 'oneof', False),
+            ('erbottleabc', 'waterbottle', False),
+            ('ion?rotat', 'rotation?', True),
+            ('', '', True),
+            ('a', 'a', True),
+            ('a', 'b', False),
+            ('erbottlewat', 'eeeeeeeeee', False)
+        ]
+
+        self.is_substring_cases = [
+            ('swag', 'swagger', True),
+            ('swagger', 'swag', False),
+            ('test', 'testing', True),
+            ('', 'sdfkjslf', True),
+            ('abcd', 'defg', False)
+        ]
+
+    def test_is_substring(self):
+        for sub, s, expected in self.is_substring_cases:
+            self.assertEqual(is_substring(sub, s), expected, msg=(sub, s, expected))
+
+    def test_string_rotation(self):
+        for s1, s2, expected in self.str_rotation_cases:
+            self.assertEqual(string_rotation(s1, s2), expected, msg=(s1, s2, expected))
+
+
+if __name__ == '__main__':
+    unittest.main()