Google STEP 2017: Code Readability, Code Review (with NP)

Hayato Ito (hayato@google.com)

Travelling Salesman Problem Challenges

Quick Links

• Scoreboard
• GitHub Issues

Problem Statement

In this assignment, you will design an algorithm to solve a fundamental problem faced by every travelling salesperson, called Travelling Salesman Problem (TSP). I’ll explain TSP in the onsite class. TSP is very famous problem. See Wikipedia. You can understand the problem without any difficulties.

Quoted from Wikipedia:

The travelling salesman problem (TSP) asks the following question: Given a list of cities and the distances between each pair of cities, what is the shortest possible route that visits each city exactly once and returns to the origin city?

Assignment

The assignment is hosted on GitHub, https://github.com/hayatoito/google-step-tsp. You can download the assignment by git clone:

git clone https://github.com/hayatoito/google-step-tsp
git checkout gh-pages

I recommend you to fork this repository to your github account before cloning it.

This document doesn't explain “what is git?’ nor “how to use GitHub?”. It is your responsibility to master the usage of git and GitHub.

The repository includes sample scripts written in Python 3, rather than in Python 2. It’s your responsibility to install Python 3 if you want to run the scripts, though running the scripts is not mandatory.

There are 7 challenges of TSP in the assignment, from N = 5 to N = 2048:

Challenge	N (= the number of cities)	Input file	Output (Solution) file
Challenge 0	5	input_0.csv	solution_yours_0.csv
Challenge 1	8	input_1.csv	solution_yours_1.csv
Challenge 2	16	input_2.csv	solution_yours_2.csv
Challenge 3	64	input_3.csv	solution_yours_3.csv
Challenge 4	128	input_4.csv	solution_yours_4.csv
Challenge 5	512	input_5.csv	solution_yours_5.csv
Challenge 6	2048	input_6.csv	solution_yours_6.csv

See Data Format Specification section to know the format of input and output files.

Your tasks

In coding phase:

• Write a program, solveing each TSP by designing and implementing an algorithm.
• Overwrite each solution file, solution_yours_{0-6}.csv, with the output of your program.
• Enter the path length of your solution in the scoreboard, for each challenge. Needless to say, a shorter path is better then a longer path.
• Enter your git repository's location in the scoreboard.

In review phase:

• Review other student's published code, and send at least one pull request.

An optional task (Speed challenge)

What matters in this optional task is your program's speed (execution time). The path length does not matter as long as it is meets the condition.

Your task is: Given input_6.csv, write a program which outputs a path shorter than 47,000

Input your program's execution time in the scoreboard. Faster (smaller) is better.

You can measure the execution time by time command. For example,

$ time yourprogram input_6.csv solution_yours_6.csv
2.96s user 0.07s system 97% cpu 3.116 total

In this case, your score is 3.116 (s).

Visualizer

The demo page of the visualizer is here.

The assignment includes a helper Web page, visualizer/index.html, which visualizes your solutions. You need to run a HTTP server on your local machine to access the visualizer. Any HTTP server is okay. If you are not sure how to run a web server, use the following command to run the HTTP server included in the assignment. Make sure that you are in the top directory of the assignment before running the command.

./nocache_server.py # For Python 3
./nocache_server.py2.py # If you don’t want to install Python 3

Then, open a browser and navigate to the http://localhost:8000/visualizer/.

Visualizer was only tested by Google Chrome. Using the visualizer is up-to you. You don’t have to use the visualizer to finish the assignment. The visualizer is provided for the purpose of helping you understand the problem.

Once you publish a git repository, you can also enter the URL of a visualizer for your solutions in the scoreboard (e.g. http://yourname.github.io/google-step-tsp/visualizer/).

Data Format Specification

Input Format

The input consists of N + 1 lines. The first line is always x,y. It is followed by N lines, each line represents an i-th city’s location, point xi,yi where xi, yi is a floating point number.

x,y
x_0,y_0
x_1,y_1
…
x_N-1,y_N-1

Output Format

Output has N + 1 lines. The first line should be “index”. It is followed by N lines, each line is the index of city, which represents the visitation order.

index
v_0
v_1
v_2
…
v_N-1

Example (Challenge 0, N = 5)

Input Example:

x,y
214.98279057984195,762.6903632435094
1222.0393903625825,229.56212316547953
792.6961393471055,404.5419583098643
1042.5487563564207,709.8510160219619
150.17533883877582,25.512728869805677

Output (Solution) Example:

index
0
2
3
1
4

These formats are requirements for the visualizer, which can take only properly formatted CSV files as input.

Schedule

The class begins: 2017-06-23 (Fri) 5:00pm (JST)

The class starts. You must bring your laptop.

This class is a kick-off class for the assignment, and will be basically 3 hours hackathon. You are expected to understand the problem and solve a challenge with a small N. You can also try a challenge with a large N if you can move fast in the class.

Coding phase: From: 2017-06-23 (Fri) 8:00pm - To: 2017-06-30 (Fri) 5:00pm

The deadline of the final submission is the next Friday.

Until the deadline, you are expected to improve your algorithm and enter the score in the scoreboard manually for each challenge. You can update the score as many times as needed. I highly recommend you to update your score whenever you can find a shorter path.

You can enter your git repository's location in the scoreboard once it is ready. Publish your git repository as soon as possible. Other participants want to see your code even if your code is work in progress.

You can also enter the visualizer URL so that other students can see how your salesperson is visiting each city in your solution.

Note:

• You can see and use code written in other students freely.
• Please try to publish your code as much as possible so that other students can see your code.

(Optional) Office hours: (2017-06-27 (Tue) 5:00pm)

I will hold office hours on next Tuesday at Google Tokyo office. I will be available until 9:00pm. You can come anytime and leave anytime.

How to attend office hours: I will announce it later at GitHub Issues.

(Optional) Yet another optional task: Challenge 7: 2017-06-28 (Wed)

I will announce it on 2017-06-28 (Wed) at GitHub Issues.

Review phase: From: 2017-06-30 (Fri) 5:00pm - To: 2017-07-07 (Fri) 5:00pm

The next class starts in the next Friday. we have one hour wrap-up time. You may want to bring your laptop. Be ready to explain your code and algorithm.

After the class, you have one week to review other students' code:

• You are expected to send at least one pull request in this week. Please choose any repository to where you want to send a pull request.
• You might receive a pull request from other students. Please look an incoming pull request and discuss it with a contributor, and merge the pull request to your repository if the pull request looks good to you.
• You can send any number (one or more) of pull requests to any number of repositories. That is up to you.
• When sending a pull request, please mention @hayatoito in a pull request's comment so I can notice a pull request. I'll try to join the discussion in a pull request, and might review code as I am doing in Google.

I'll announce the most valuable contributor at the end of the review phase. Please contribute to other student's repository as much as possible.

Hints

Since GitHub doesn't allow forking the same origin repository more than once into your account, the followings might be helpful to send a pull request.

Assuming that:

• You are alice. Your repository is https://github.com/alice/google-step-tsp.git

• You are trying to send a pull request to bob's repository, https://github.com/bob/google-step-tsp.git

In your google-step-tsp directory, which was cloned from https://github.com/alice/google-step-tsp.git, do the followings:

# Add and fetch bob's repository
git remote add bob https://github.com/bob/google-step-tsp.git
git fetch bob

# See bob's branches
git branches -a

# Create a local branch, bob-gh-pages, from bob's remote branch, bob/gh-pages
git checkout -b bob-gh-pages bob/gh-pages

# Work on local bob-gh-pages branch, as usual
....

# When it is ready, push the bob-gh-pages branch to your repository, https://github.com/alice/google-step-tsp.git
# Your repository is usually called 'origin'.
git push origin bob-gh-pages

# Create a pull request at https://github.com/alice/google-step-tsp.git with:
# base fork: bob/google-step-tsp, base: gh-pages  .... head fork: alice/google-step-tsp, compare: bob-gh-pages

What’s included in the assignment

To help you understand the problem, there are some sample scripts / resources in the assignment, including, but not limited to:

• solver_random.py - Sample stupid solver. You never lose to this stupid one.
• solution_random_{0-6}.csv - Sample solutions by solver_random.py.
• solver_greedy.py - Sample solver using the greedy algorithm. You should beat this definitely.
• solution_greedy_{0-6}.csv - Sample solutions by solver_greedy.py.
• solution_sa_{0-6}.csv - Yet another sample solutions. I expect all of you will beat this one too. The solver itself is not included intentionally.
• solution_yours_{0-6}.csv - You should overwrite these files with your solution.
• solution_verifier.py - Try to validate your solution and print the path length.
• input_generator.py - Python script which was used to create input files, input_{0-6}.csv
• visualizer/ - The directory for visualizer.

Details are intentionally omitted here. It is your responsibility to understand the contents of the repository.

Discussions / Collaboration Rules / Code of Conduct

Discussion

• I highly encourage you to exchange an idea between students. If you have any question, or any idea, please share it at GitHub Issues. It is very important to share your question among all students so that everyone can get benefits from the discussion there. Other students may have the same question. Please feel free to answer a question from other students. I will join the discussion as much as possible.

• You might want to watch the repository so that you get a notification when new question is posted.

Group

• It is okay to work as a group if you prefer. The number of members in one group should be less than 5. Please use one GitHub repository per a group. You should mention who are the members in README.md file.

Code of Conduct

• You can get an assistance only from other STEP students or me. Please refrain from getting an assistance from any other person.
• Use your best judgment when using third party libraries. No one wants to review code which just uses third-party libraries.
• It is okay to use built-in libraries provided by programming languages.

Please see also code of conduct, if you are interested in, as a general code of conduct, as a reference.

Feedback from me

I will make my best effort to answer your questions via:

• GitHub Issues for this class.

• Office hours

I will review your code and give you a comment as much as possible, if all of the following conditions are satisfied:

• Your code is hosted on GitHub. I will use GitHub's code review system.

• Your code is consistency well formatted. I don't see code which is not well formatted. That is one of pre-requirement to get your code be reviewed, in general. Please make sure to use appropriate code formatter, if you are not in confident.

• Your code is written in one of the followings: C++, Rust, Scala, Python3, Python2, Java, C, JavaScript, Haskell, OCaml, and Lisp. I can't promise to review your code if the code is written in other programming languages.

Please feel free to mention @hayatoito at GitHub anytime if you need my help. I will get notified. I will make my best effort to give a comment on your code.

I will not comment much about your approach itself. I will comment mainly about the quality of your code, in terms of readability and efficiency (time and space).

You can also comment on other student's code at GitHub. Please get familiar with Git and GitHub, and use them effectively as a collaboration tool.

FAQ

This FAQ includes the questions and the answers in the past years, as is. Some Q/A might be obsolete for this year. Please use GitHub Issues for a new question.

• Q. I found a typo in this document.

• A. Please feel free to send a pull request or file an issue at GitHub Issues to improve this document.

• Q. Can I use any programming language?

• A. Yes. It’s one of the most important skills to choose an appropriate programming language case by case.

• Q. Do I have to use the same code for every challenges?

• A. No.

• Q. Is there any limitation of machine resources I can use? Can I use multiple machines? Can I run my algorithm 24 hours?

• A. No limitation at all. You can use any machine resources you have.

• Q. It seems that this document and the scoreboard are publicly viewable. Is this intentional?

• A. Yes. I am a fan of transparency. If you have any concerns, please let me know that. I’ll honor your preference. Don’t enter any confidential information.

• Q. Visualizer does not work well on firefox (or any other browsers you are using)

• A. I appreciate if you could send a pull request which fixes the issue. You can consider this as an optional assignment. Your contribution is highly welcome.

Acknowledgments

This assignment is heavily inspired by Discrete Optimization Course on Coursera.