Number of 1 Bits

EasyBit Manipulation

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Problem

Given an unsigned 32-bit integer, return the number of '1' bits it has (also known as the Hamming weight).

Examples

Example 1

Input:n = 11 (binary 1011)

Output:3

Example 2

Input:n = 128 (binary 10000000)

Output:1

Constraints

The input is a 32-bit unsigned integer.

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How to approach it: the Bit Manipulation pattern

Work directly on a number's binary representation using bitwise operators — often turning an O(n) or O(log n) problem into a handful of O(1) operations.

Look for this pattern when

The problem talks about bits directly (count set bits, reverse bits, single number among duplicates).
You want a constant-time trick instead of a loop for a numeric problem.

Read the full Bit Manipulation guide →

Video walkthroughs

Original problem on LeetCode ↗