From bb078541dd030b4957ee1b5ac87b7a31bf1a7235 Mon Sep 17 00:00:00 2001
From: JatinR05 <71865805+JatinR05@users.noreply.github.com>
Date: Mon, 24 Oct 2022 15:43:39 +0530
Subject: [PATCH] Update count_number_of_one_bits.py (#7589)

* Update count_number_of_one_bits.py

removed the modulo operator as it is very time consuming in comparison to the and operator

* Update count_number_of_one_bits.py

Updated with the timeit library to compare. Moreover I have updated my code which helps us in reaching the output comparatively faster.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update bit_manipulation/count_number_of_one_bits.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update count_number_of_one_bits.py

Updated the code

* Update count_number_of_one_bits.py

Updated code

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Run the tests before running the benchmarks

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* consistently

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>
---
 bit_manipulation/count_number_of_one_bits.py | 79 +++++++++++++++++---
 1 file changed, 68 insertions(+), 11 deletions(-)

diff --git a/bit_manipulation/count_number_of_one_bits.py b/bit_manipulation/count_number_of_one_bits.py
index 51fd2b630..a1687503a 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()