Create is_power_of_three.py

maths/is_power_of_three.py

@@ -0,0 +1,41 @@
+"""
+Check if an integer is a power of three.
+
+Time Complexity: O(log₃ n)
+Space Complexity: O(1)
+"""
+
+
+def is_power_of_three(n: int) -> bool:
+    """Return True if n is a power of three (n > 0).
+
+    >>> is_power_of_three(1)
+    True
+    >>> is_power_of_three(3)
+    True
+    >>> is_power_of_three(9)
+    True
+    >>> is_power_of_three(27)
+    True
+    >>> is_power_of_three(2)
+    False
+    >>> is_power_of_three(0)
+    False
+    >>> is_power_of_three(-3)
+    False
+    >>> is_power_of_three(81)
+    True
+    """
+    if not isinstance(n, int):
+        raise TypeError("n must be an integer")
+    if n <= 0:
+        return False
+    while n % 3 == 0:
+        n //= 3
+    return n == 1
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()