What are the most useful bit manipulation tricks for interviews?

Q: What are the most useful bit manipulation tricks for interviews?

**Target Audience:** Developers preparing for coding interviews who are comfortable with loops and integers in Python; binary is explained from scratch. **Difficulty:** Medium **Language:** Python 3 > **How to read this doc:** every idea is explained in plain words first. When a word appears that an interviewer will expect you to know, it is tagged `📌 Interview term:` with a one-line definition, and every tagged term is collected in the Quick Glossary at the end. Every program on this page was actually run, and the output you see in the **Verified** section is copied from that run. ## 1. Why This Even Matters — A Story First Picture the light-switch panel in a small office: eight switches in a row, each controlling one room. To answer "is the kitchen light on?" you look at one switch. To turn the meeting room on without touching anything else, you flip only that switch. To ask "how many rooms are lit?" you count the switches that are up. An integer inside a computer is exactly

The problem

Question presented to candidate: "Walk me through the bit manipulation tricks you would actually use in a coding interview. For each, tell me the expression, why it works, and anything about Python integers that changes how you write it."

What a strong answer should cover:

The single-bit operations with a mask: test (x >> i) & 1, set x | (1 << i), clear x & ~(1 << i), toggle x ^ (1 << i).
The lowest-set-bit pair: x & (x - 1) clears it, x & -x isolates it; the power-of-two test with the x > 0 guard.
XOR properties (a ^ a == 0, a ^ 0 == a) and their uses: single number, missing number, Hamming distance.
Bitmasks as sets: enumerate subsets with range(1 << n), submasks with sub = (sub - 1) & mask, and the 3^n total.
Python details: ints are unbounded (no overflow, no >>>), negatives act like infinite leading 1s so you mask with & 0xFFFFFFFF to emulate 32 bits, int.bit_count() (3.10+) and int.bit_length(), and & binds tighter than == in Python (unlike C-family languages).

Code / implementation expected: Optional — short Python expressions for each trick, ideally with a small demo on one number.

dsa
bit-manipulation

Try it yourself

Sketch your approach before you read the solution. That is what the interview tests.

Stuck? Get a hint.

A short nudge toward the approach. It will not give the answer away.

Solution

Target Audience: Developers preparing for coding interviews who are comfortable with loops and integers in Python; binary is explained from scratch.
Difficulty: Medium
Language: Python 3

How to read this doc: every idea is explained in plain words first. When a word appears that an interviewer will expect you to know, it is tagged 📌 Interview term: with a one-line definition, and every tagged term is collected in the Quick Glossary at the end. Every program on this page was actually run, and the output you see in the Verified section is copied from that run.

1. Why This Even Matters — A Story First

Picture the light-switch panel in a small office: eight switches in a row, each controlling one room. To answer "is the kitchen light on?" you look at one switch. To turn the meeting room on without touching anything else, you flip only that switch. To ask "h

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10 min read · 15 sections

Python code

Edit the code and run it here. Each printed line with an expected value becomes a test.

PythonSingle-bit and lowest-bit tricks on x = 44

Practice

PythonBitmasks as sets: subsets, set operations, submasks, 3^n

Practice

PythonEmulating 32-bit integers in Python

Practice

Discussion

Other approaches, follow-ups and how it went in real interviews.

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