Power of 4

bit_manipulation/power_of_4.py

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+"""
+
+Task:
+Given a positive int number. Return True if this number is power of 4
+or False otherwise.
+
+Implementation notes: Use bit manipulation.
+For example if the number is the power of 2 it's bits representation:
+n = 0..100..00
+n - 1 = 0..011..11
+
+n & (n - 1) - no intersections = 0
+If the number is a power of 4 then it should be a power of 2
+and the set bit should be at an odd position.
+"""
+
+
+def power_of_4(number: int) -> bool:
+ """
+ Return True if this number is power of 4 or False otherwise.
+
+ >>> power_of_4(0)
+ Traceback (most recent call last):
+ ...
+ ValueError: number must be positive
+ >>> power_of_4(1)
+ True
+ >>> power_of_4(2)
+ False
+ >>> power_of_4(4)
+ True
+ >>> power_of_4(6)
+ False
+ >>> power_of_4(8)
+ False
+ >>> power_of_4(17)
+ False
+ >>> power_of_4(64)
+ True
+ >>> power_of_4(-1)
+ Traceback (most recent call last):
+ ...
+ ValueError: number must be positive
+ >>> power_of_4(1.2)
+ Traceback (most recent call last):
+ ...
+ TypeError: number must be an integer
+
+ """
+ if not isinstance(number, int):
+ raise TypeError("number must be an integer")
+ if number <= 0:
+ raise ValueError("number must be positive")
+ if number & (number - 1) == 0:
+ c = 0
+ while number:
+ c += 1
+ number >>= 1
+ return c % 2 == 1
+ else:
+ return False
+
+
+if __name__ == "__main__":
+ import doctest
+
+ doctest.testmod()