diff --git a/bit_manipulation/count_1s_brian_kernighan_method.py b/bit_manipulation/count_1s_brian_kernighan_method.py new file mode 100644 index 000000000..d217af90b --- /dev/null +++ b/bit_manipulation/count_1s_brian_kernighan_method.py @@ -0,0 +1,43 @@ +def get_1s_count(number: int) -> int: + """ + Count the number of set bits in a 32 bit integer using Brian Kernighan's way. + Ref - http://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()