interactive-coding-challenges

Continually updated, interactive and test-driven coding challenges.

Challenges focus on algorithms and data structures that are typically found in coding interviews.

Each challenge has one or more reference solutions that are:

• Fully functional
• Unit tested
• Easy-to-understand

Challenges will soon provide on-demand incremental hints to help you arrive at the optimal solution.

Notebooks also detail:

• Constraints
• Test cases
• Algorithms
• Big-O time and space complexities

Challenge Solutions

Notebook Structure

Each challenge has two notebooks, a challenge notebook for you to solve and a solution notebook for reference.

Problem Statement

• States the problem to solve.

Constraints

• Describes any constraints or assumptions.

Test Cases

• Describes the general and edge test cases that will be evaluated in the unit test.

Algorithm

• [Challenge Notebook] Empty, refer to the solution notebook algorithm section if you need a hint.
• [Solution Notebook] One or more algorithm solution discussions, with Big-O time and space complexities.

Hints

• [Challenge Notebook] Provides on-demand incremental hints to help you arrive at the optimal solution. Coming soon!

Code (Challenge: Implement Me!)

• [Challenge Notebook] Skeleton code for you to implement.
• [Solution Notebook] One or more reference solutions.

Unit Test

• [Challenge Notebook] Unit test for your code. Expected to fail until you solve the challenge.
• [Solution Notebook] Unit test for the reference solution(s).

Future Development

Challenges, solutions, and unit tests are presented in the form of IPython/Jupyter Notebooks.

• Notebooks currently contain mostly Python solutions (tested on both Python 2.7 and Python 3.4), but can be extended to include 44 supported languages
• Repo will be continually updated with new solutions and challenges
• Contributions are welcome!

Index

Challenges Categories

• Arrays and Strings
• Linked Lists
• Stacks and Queues
• Sorting
• Graphs and Trees
• Recursion and Dynamic Programming
• Bit Manipulation
• Scalability and Memory Limits
• Concurrency
• Online Judges

Installing and Running Challenges

• Repo Structure
• Notebook Installation
  • Nose Installation
• Running Challenges

Misc

• Contributing
• Credits
• Contact Info
• License

Challenges

Image Credits

Arrays and Strings

Challenge	Static Notebook
Determine if a string contains unique characters	Challenge│Solution
Determine if a string is a permutation of another	Challenge│Solution
Determine if a string is a rotation of another	Challenge│Solution
Compress a string	Challenge│Solution
Reverse characters in a string	Challenge│Solution
Implement a hash table	Challenge│Solution
Find the first non-repeated character in a string	Contribute│Contribute
Remove specified characters in a string	Contribute│Contribute
Reverse words in a string	Contribute│Contribute
Convert a string to an integer	Contribute│Contribute
Convert an integer to a string	Contribute│Contribute
Add a challenge	Contribute│Contribute

Linked Lists

Challenge	Static Notebook
Remove duplicates from a linked list	Challenge│Solution
Find the kth to last element of a linked list	Challenge│Solution
Delete a node in the middle of a linked list	Challenge│Solution
Partition a linked list around a given value	Challenge│Solution
Add two numbers whose digits are stored in a linked list	Challenge│Solution
Find the start of a linked list loop	Challenge│Solution
Determine if a linked list is a palindrome	Challenge│Solution
Implement a linked list	Challenge│Solution
Determine if a list is cyclic or acyclic	Contribute│Contribute
Add a challenge	Contribute│Contribute

Stacks and Queues

Challenge	Static Notebook
Implement n stacks using a single array	Challenge│Solution
Implement a stack that keeps track of its minimum element	Challenge│Solution
Implement a set of stacks class that wraps a list of capacity-bounded stacks	Challenge│Solution
Implement a queue using two stacks	Challenge│Solution
Sort a stack using another stack as a buffer	Challenge│Solution
Implement a stack	Challenge│Solution
Implement a queue	Challenge│Solution
Add a challenge	Contribute│Contribute

Sorting

Challenge	Static Notebooks
Implement selection sort	Challenge│Solution
Implement insertion sort	Challenge│Solution
Implement quick sort	Challenge│Solution
Implement merge sort	Challenge│Solution
Implement a stable selection sort	Contribute│Contribute
Make an unstable sort stable	Contribute│Contribute
Implement an efficient, in-place version of quicksort	Contribute│Contribute
Given two sorted arrays, merge one into the other in sorted order	Contribute│Contribute
Sort an array of strings so all anagrams are next to each other	Contribute│Contribute
Find an element in a rotated and sorted array of integers	Contribute│Contribute
Add a challenge	Contribute│Contribute

Graphs and Trees

Challenge	Static Notebooks
Implement depth-first search (pre-, in-, post-order) on a tree	Challenge│Solution
Implement breadth-first search on a tree	Challenge│Solution
Determine the height of a tree	Challenge│Solution
Create a binary search tree with minimal height from a sorted array	Challenge│Solution
Create a linked list for each level of a binary tree	Challenge│Solution
Check if a binary tree is balanced	Challenge│Solution
Determine if a tree is a valid binary search tree	Challenge│Solution
Find the in-order successor of a given node in a binary search tree.	Challenge│Solution
Implement a binary search tree	Challenge│Solution
Implement depth-first search on a graph	Challenge│Solution
Implement breadth-first search on a graph	Challenge│Solution
Determine if there is a path between two nodes in a graph	Challenge│Solution
Implement a graph	Challenge│Solution
Print a tree using pre-order traversal without recursion	Contribute│Contribute
Determine the lowest common ancestor of two nodes	Contribute│Contribute
Transform a binary tree into a heap	Contribute│Contribute
Implement a right and left rotation on a tree	Contribute│Contribute
Check if a binary tree is binary search tree	Contribute│Contribute
Add a challenge	Contribute│Contribute

Recursion and Dynamic Programming

Challenge	Static Notebooks
Implement fibonacci recursively, dynamically, and iteratively	Challenge│Solution
Implement the Towers of Hanoi with 3 towers and N disks	Challenge│Solution
Find the number of ways to represent n cents given an array of coins	Challenge│Solution
Print all valid combinations of n-pairs of parentheses	Challenge│Solution
Implement factorial recursively, dynamically, and iteratively	Contribute│Contribute
Perform a binary search on a sorted array of integers	Contribute│Contribute
Print all subsets of a set	Contribute│Contribute
Print all permutations of a string	Contribute│Contribute
Print all combinations of a string	Contribute│Contribute
Implement a paint fill function	Contribute│Contribute
Find all permutations to represent n cents, given 1, 5, 10, 25 cent coins	Contribute│Contribute
Add a challenge	Contribute│Contribute

Mathematics and Probability

Challenge	Static Notebooks
Check if a number is prime	Contribute│Contribute
Generate a list of primes	Contribute│Contribute
Determine if two lines on a Cartesian plane intersect	Contribute│Contribute
Using only add, implement multiply, subtract, and divide for ints	Contribute│Contribute
Find the kth number such that the only prime factors are 3, 5, and 7	Contribute│Contribute
Add a challenge	Contribute│Contribute

Bit Manipulation

Challenge	Static Notebooks
Given a number between 0 and 1, print the binary representation	Contribute│Contribute
Determine the number of bits required to convert integer A to integer B	Contribute│Contribute
Swap odd and even bits in an integer with as few instructions as possible	Contribute│Contribute
Determine the number of 1 bits in the binary representation of a given integer	Contribute│Contribute
Add a challenge	Contribute│Contribute

Online Judges

Challenge	Static Notebooks
Utopian tree	Challenge│Solution
Maximizing xor	Challenge│Solution
Add a challenge	Contribute│Contribute

Repo Structure

interactive-coding-challenges        # Repo
├─ arrays_strings                    # Category of challenges
│  ├─ rotation                       # Challenge folder
│  │  ├─ rotation_challenge.ipynb    # Challenge notebook
│  │  ├─ rotation_solution.ipynb     # Solution notebook
│  │  ├─ test_rotation.py            # Unit test*
│  ├─ compress
│  │  ├─ compress_challenge.ipynb
│  │  ├─ compress_solution.ipynb
│  │  ├─ test_compress.py
│  ├─ ...
├─ linked_lists
│  ├─ palindrome
│  │  └─ ...
│  ├─ ...
├─ ...

*The notebooks (.pynb) read/write the associated unit test (.py) file.

Notebook Installation

IPython Notebook

If you already have Python installed and are familiar with installing packages, you can get IPython Notebook with pip:

pip install "ipython[notebook]"

If you run into an issue about pyzmq, refer to the following Stack Overflow post and run:

pip uninstall ipython
pip install "ipython[all]"

As an alternative, you can also use the provided requirements.txt file:

pip install -r requirements.txt

For detailed instructions, scripts, and tools to more optimally set up your development environment, check out the dev-setup repo.

For more details on notebook installation, follow the directions here.

More information on IPython/Jupyter Notebooks can be found here.

Nose Tests

Install nose using setuptools/distribute:

easy_install nose

or

pip install nose

More information on Nose can be found here.

Running Challenges

Notebooks

Challenges are provided in the form of IPython/Jupyter Notebooks and have been tested with Python 2.7 and Python 3.4.

If you need to install IPython/Jupyter Notebook, see the Notebook Installation section.

• This README contains links to nbviewer, which hosts static notebooks of the repo's contents
• To interact with or to modify elements within the dynamic notebooks, refer to the instructions below

Run the notebook of challenges:

$ git clone https://github.com/donnemartin/interactive-coding-challenges.git
$ cd interactive-coding-challenges
$ jupyter notebook

This will launch your web browser with the list of challenge categories:

• Navigate to the Challenge Notebook you wish to solve
• Run the cells within the challenge notebook (Cell->Run All)
  • This will result in an expected unit test error
• Solve the challenge and verify it passes the unit test
• Check out the accompanying Solution Notebook for further discussion

To debug your solution with pdb, refer to the following ticket.

Note: If your solution is different from those listed in the Solution Notebook, consider submitting a pull request so others can benefit from your work. Review the Contributing Guidelines for details.

Contributing

Contributions are welcome!

Review the Contributing Guidelines for details on how to:

• Submit issues
• Add solutions to existing challenges
• Add new challenges

Credits

Resources

• Cracking the Coding Interview | GitHub Solutions
• Elements of Programming Interviews | GitHub Solutions
• Programming Interviews Exposed
• The Algorithm Design Manual | Solutions
• CareerCup
• Quora
• HackerRank
• LeetCode
• TopCoder

Images

• Arrays and Strings: nltk.org
• Linked Lists: wikipedia.org
• Stacks: wikipedia.org
• Queues: wikipedia.org
• Sorting: wikipedia.org
• Recursion and Dynamic Programming: wikipedia.org
• Graphs and Trees: wikipedia.org
• Mathematics and Probability: wikipedia.org
• Bit Manipulation: wikipedia.org
• Online Judges: topcoder.com

Contact Info

Feel free to contact me to discuss any issues, questions, or comments.

My contact info can be found on my GitHub page.

License

Copyright 2015 Donne Martin

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.