diff --git a/bit_manipulation/count_number_of_one_bits.py b/bit_manipulation/count_number_of_one_bits.py index 51fd2b630483..a1687503a383 100644 --- a/bit_manipulation/count_number_of_one_bits.py +++ b/bit_manipulation/count_number_of_one_bits.py @@ -1,34 +1,91 @@ -def get_set_bits_count(number: int) -> int: +from timeit import timeit + + +def get_set_bits_count_using_brian_kernighans_algorithm(number: int) -> int: """ Count the number of set bits in a 32 bit integer - >>> get_set_bits_count(25) + >>> get_set_bits_count_using_brian_kernighans_algorithm(25) 3 - >>> get_set_bits_count(37) + >>> get_set_bits_count_using_brian_kernighans_algorithm(37) 3 - >>> get_set_bits_count(21) + >>> get_set_bits_count_using_brian_kernighans_algorithm(21) 3 - >>> get_set_bits_count(58) + >>> get_set_bits_count_using_brian_kernighans_algorithm(58) 4 - >>> get_set_bits_count(0) + >>> get_set_bits_count_using_brian_kernighans_algorithm(0) 0 - >>> get_set_bits_count(256) + >>> get_set_bits_count_using_brian_kernighans_algorithm(256) 1 - >>> get_set_bits_count(-1) + >>> get_set_bits_count_using_brian_kernighans_algorithm(-1) Traceback (most recent call last): ... - ValueError: the value of input must be positive + ValueError: the value of input must not be negative """ if number < 0: - raise ValueError("the value of input must be positive") + raise ValueError("the value of input must not be negative") + result = 0 + while number: + number &= number - 1 + result += 1 + return result + + +def get_set_bits_count_using_modulo_operator(number: int) -> int: + """ + Count the number of set bits in a 32 bit integer + >>> get_set_bits_count_using_modulo_operator(25) + 3 + >>> get_set_bits_count_using_modulo_operator(37) + 3 + >>> get_set_bits_count_using_modulo_operator(21) + 3 + >>> get_set_bits_count_using_modulo_operator(58) + 4 + >>> get_set_bits_count_using_modulo_operator(0) + 0 + >>> get_set_bits_count_using_modulo_operator(256) + 1 + >>> get_set_bits_count_using_modulo_operator(-1) + Traceback (most recent call last): + ... + ValueError: the value of input must not be negative + """ + if number < 0: + raise ValueError("the value of input must not be negative") result = 0 while number: if number % 2 == 1: result += 1 - number = number >> 1 + number >>= 1 return result +def benchmark() -> None: + """ + Benchmark code for comparing 2 functions, with different length int values. + Brian Kernighan's algorithm is consistently faster than using modulo_operator. + """ + + def do_benchmark(number: int) -> None: + setup = "import __main__ as z" + print(f"Benchmark when {number = }:") + print(f"{get_set_bits_count_using_modulo_operator(number) = }") + timing = timeit("z.get_set_bits_count_using_modulo_operator(25)", setup=setup) + print(f"timeit() runs in {timing} seconds") + print(f"{get_set_bits_count_using_brian_kernighans_algorithm(number) = }") + timing = timeit( + "z.get_set_bits_count_using_brian_kernighans_algorithm(25)", + setup=setup, + ) + print(f"timeit() runs in {timing} seconds") + + for number in (25, 37, 58, 0): + do_benchmark(number) + print() + + if __name__ == "__main__": import doctest doctest.testmod() + benchmark()