number-of-1-bits

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Algorithms

Given a positive integer <code>n</code>, write a function that returns the number of set bits in its binary representation (also known as the <a href="http://en.wikipedia.org/wiki/Hamming_weight" target="_blank">Hamming weight</a>).

&nbsp;
Example 1:

<div class="example-block">
Input: n = 11

Output: 3

Explanation:

The input binary string 1011 has a total of three set bits.
</div>

Example 2:

<div class="example-block">
Input: n = 128

Output: 1

Explanation:

The input binary string 10000000 has a total of one set bit.
</div>

Example 3:

<div class="example-block">
Input: n = 2147483645

Output: 30

Explanation:

The input binary string 1111111111111111111111111111101 has a total of thirty set bits.
</div>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= n &lt;= 231 - 1</code></li>
</ul>

&nbsp;
Follow up: If this function is called many times, how would you optimize it?