Strings: rotation

Author: tomaslink

src/algorithmic/arrays.py

@@ -6,7 +6,7 @@ def rotate_matrix(matrix: List[List]) -> None:
 
     Complexity:
     - Time: O(N^2)
-    - Space: O(N^2)
+    - Space: O(1)
     """
     if len(matrix) != len(matrix[0]):
         raise ValueError("Input matrix must be square.")

src/algorithmic/strings.py

@@ -227,3 +227,20 @@ def compression(string: str) -> str:
         return string
 
     return compressed
+
+
+def rotation(s1: str, s2: str) -> str:
+    """Checks if string s2 is a rotation of string s1, e.g.,
+        "erbottlewat" is a rotation of "waterbottle".
+
+    Complexity:
+    - Time: O(A + B)
+    - Space: O(A + B)
+
+    Where A, B are the lengths of s1 and s2, respectively,
+        assuming sub-string check has O(A + B) time.
+    """
+    if len(s1) != len(s2) or len(s1) == 0:
+        return False
+
+    return s1 in ''.join([s2, s2])

tests/test_strings.py

@@ -75,3 +75,11 @@ def test_compression():
     assert strings.compression("AABCCCCCAAA") == "A2B1C5A3"
     assert strings.compression("ABBACCC") == "A1B2A1C3"
     assert strings.compression("AA") == "AA"
+
+
+def test_rotation():
+    assert strings.rotation("waterbottle", "erbottlewat")
+    assert not strings.rotation("waterbottle", "notarotation")
+
+    assert not strings.rotation("waterbottle", "w")
+    assert not strings.rotation("", "")