Leetcode #2595: Number of Even and Odd Bits

In this guide, we solve Leetcode #2595 Number of Even and Odd Bits in Python and focus on the core idea that makes the solution efficient.

You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.

Problem Statement

You are given a positive integer n. Let even denote the number of even indices in the binary representation of n with value 1.

Quick Facts

• Difficulty: Easy
• Premium: No
• Tags: Bit Manipulation

Intuition

The problem structure lets us track state with bitwise operations.

Bit operations are constant time and avoid extra memory.

Approach

Apply XOR/AND/OR and shifts to maintain the required invariant.

Aggregate the result in a single pass.

Steps:

• Identify a bitwise invariant.
• Combine values with bit operations.
• Return the aggregated result.

Python Solution

Complexity

The time complexity is $O(\log n)$ and the space complexity is $O(1)$. The space complexity is $O(1)$.

Edge Cases and Pitfalls

Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.

Summary

This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.