Python Interview Solutions

A growing collection of Python interview problems explained from first principles.

Each solution includes:

• The original problem contract
• Intuition and pattern recognition
• A step-by-step approach
• Complexity analysis
• A worked dry run
• Clean, executable Python
• Focused test cases

The purpose of this repository is not to claim novel algorithms. It documents how I understand, explain, implement, and test common interview patterns.

Problem Index

#	Problem	Pattern	Difficulty	Time	Space
1	Two Sum	Hash map	Easy	O(n)	O(n)
13	Roman to Integer	Hash map and scan	Easy	O(n)	O(1)
14	Longest Common Prefix	String scanning	Easy	O(S)	O(1)
20	Valid Parentheses	Stack	Easy	O(n)	O(n)

S is the total number of characters inspected across all input strings.

Run the Tests

The repository uses only Python's standard library.

python3 -m unittest discover -s tests -v

Repository Structure

python-interview-solutions/
├── problems/
│   ├── 0001-two-sum/
│   ├── 0013-roman-to-integer/
│   ├── 0014-longest-common-prefix/
│   └── 0020-valid-parentheses/
├── tests/
└── README.md

Learning Method

For every problem, I follow the same sequence:

1. Restate the input and output.
2. Walk through a small example.
3. Describe a correct brute-force approach.
4. Identify repeated work or a useful ordering property.
5. Select the appropriate data structure.
6. Implement and test the optimized solution.
7. State time and auxiliary-space complexity.

Disclaimer

Problem names and descriptions refer to common programming-interview exercises. Explanations and implementations in this repository are written for personal learning and interview preparation.