From d28463c75df4dbaee795c99c05a4021d4cc5e386 Mon Sep 17 00:00:00 2001
From: Jainendra Mandavi <jainendra@users.noreply.github.com>
Date: Mon, 18 Oct 2021 22:23:10 +0530
Subject: [PATCH] Create count_1s_brian_kernighan_method (#5385)

Ref - http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan
---
 .../count_1s_brian_kernighan_method.py        | 43 +++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 bit_manipulation/count_1s_brian_kernighan_method.py

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()