:orphan:

Number of 1 Bits
================

.. highlight:: none

Problem
-------
https://leetcode.com/problems/number-of-1-bits/

Write a function that takes the binary representation of a positive
integer and returns the number of **set bits** it has (also known as
the `Hamming weight <https://en.wikipedia.org/wiki/Hamming_weight>`_).



**Example 1:**

::

   Input: n = 11
   Output: 3
   Explanation: The input binary string 1011 has a total of three set bits.

**Example 2:**

::

   Input: n = 128
   Output: 1
   Explanation: The input binary string 10000000 has a total of one set bit.

**Example 3:**

::

   Input: n = 2147483645
   Output: 30
   Explanation: The input binary string 1111111111111111111111111111101 has a total of thirty set bits.



**Constraints:**

- ``1 <= n <= 2``\ :sup:`31`\ ``- 1``

.. highlight:: python

Pattern
-------
Bit Manipulation

Approaches
----------

.. tab-set::

    .. tab-item:: Bit Scan

        **Code**

        .. literalinclude:: ../problems/medium/number-of-1-bits/number_of_1_bits__bit_scan.py
            :language: python
            :lines: 12-

        **Test**

        >>> from number_of_1_bits__bit_scan import hammingWeight
        >>> hammingWeight(11)
        3
        >>> hammingWeight(128)
        1
        >>> hammingWeight(2147483645)
        30

        .. autofunction:: number_of_1_bits__bit_scan.hammingWeight

    .. tab-item:: Brian Kernighan

        **Code**

        .. literalinclude:: ../problems/medium/number-of-1-bits/number_of_1_bits__brian_kernighan.py
            :language: python
            :lines: 12-

        **Test**

        >>> from number_of_1_bits__brian_kernighan import hammingWeight
        >>> hammingWeight(11)
        3
        >>> hammingWeight(128)
        1
        >>> hammingWeight(2147483645)
        30

        .. autofunction:: number_of_1_bits__brian_kernighan.hammingWeight