Python/bit_manipulation/count_1s_brian_kernighan_method.py
2022-10-16 15:45:25 +02:00

44 lines
1.2 KiB
Python

def get_1s_count(number: int) -> int:
"""
Count the number of set bits in a 32 bit integer using Brian Kernighan's way.
Ref - https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan
>>> get_1s_count(25)
3
>>> get_1s_count(37)
3
>>> get_1s_count(21)
3
>>> get_1s_count(58)
4
>>> get_1s_count(0)
0
>>> get_1s_count(256)
1
>>> get_1s_count(-1)
Traceback (most recent call last):
...
ValueError: the value of input must be positive
>>> get_1s_count(0.8)
Traceback (most recent call last):
...
TypeError: Input value must be an 'int' type
"""
if number < 0:
raise ValueError("the value of input must be positive")
elif isinstance(number, float):
raise TypeError("Input value must be an 'int' type")
count = 0
while number:
# This way we arrive at next set bit (next 1) instead of looping
# through each bit and checking for 1s hence the
# loop won't run 32 times it will only run the number of `1` times
number &= number - 1
count += 1
return count
if __name__ == "__main__":
import doctest
doctest.testmod()