> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Reverse Bits Python Solution with Tests

> Tested Python solution for LeetCode 190 with 16 pytest cases. Generate a practice environment with lcpy.

LeetCode 190, Easy. Topics: Divide and Conquer, Bit Manipulation. [View on LeetCode](https://leetcode.com/problems/reverse-bits/description/).

Generate this problem as a practice environment: tested reference solution, 16 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 190   # by problem number
lcpy gen -s reverse_bits   # by problem name
```

## Problem

Reverse bits of a given 32 bits signed integer.

### Examples

```
Input: n = 43261596
Output: 964176192
Explanation:

| Integer    | Binary                              |
|------------|-------------------------------------|
| 43261596   | 00000010100101000001111010011100    |
| 964176192  | 00111001011110000010100101000000    |
```

```
Input: n = 2147483644
Output: 1073741822
Explanation:

| Integer     | Binary                              |
|-------------|-------------------------------------|
| 2147483644  | 01111111111111111111111111111100    |
| 1073741822  | 00111111111111111111111111111110    |
```

### Constraints

* 0 \<= n \<= 2^31 - 2
* n is even.

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

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/reverse_bits/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/reverse_bits/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(1) - always 32 iterations
    # Space: O(1) - only using constant extra space
    def reverse_bits(self, n: int) -> int:
        """
        Reverse the bits of a 32-bit unsigned integer.

        Algorithm:
        1. Initialize result to 0
        2. For each of the 32 bits:
           - Extract the rightmost bit of n using (n & 1)
           - Add it to the result at the appropriate position
           - Right shift n to get the next bit
           - Left shift result to make room for the next bit
        3. Return the result

        This approach is optimal for single calls. For multiple calls,
        we could use a lookup table for optimization.
        """
        result = 0
        for _ in range(32):
            result = (result << 1) | (n & 1)
            n >>= 1
        return result
```

## Complexity

| Time                        | Space                                  |
| --------------------------- | -------------------------------------- |
| O(1) - always 32 iterations | O(1) - only using constant extra space |

## Tags

[Grind](/catalog/grind), [Blind 75](/catalog/blind-75), [NeetCode 150](/catalog/neetcode-150), [NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode).