stefansavev / demo-interview-question-merge-intervals

About

This is a simple interview problem. Demonstrates problem-solving, code-formatting, testing and Docker.

The problem is given a list of intervals, merge all the intervals which overlap. See the test cases for examples.

It comes in two flavors:

• Python
• GoLang

Getting Started

Clone the repository:

git clone https://github.com/stefansavev/demo-interview-question-merge-intervals.git

Linux/Mac users simply run

cd demo-interview-question-merge-intervals/python_merge_intervals/
export PYTHONPATH="$(cd .. && pwd)"
python ./demo.py

Windows users open a cmd.exe window and set the PYTHONPATH with

set PYTHONPATH="C:\...\demo-interview-question-merge-intervals\python_merge_intervals"

Then call python ./demo.py

Expected output:

[(2, 23), (25, 30)]

Running the tests

cd python_merge_intervals/
pytest .

to get an experience how the code works.

Expected output:

platform linux -- Python 3.8.3, pytest-6.0.2, py-1.9.0, pluggy-0.13.1
rootdir: /home/stefan/demo-interview-question-merge-intervals/python_merge_intervals
collected 5 items                                                                                                                                     

test_merge_intervals.py .....                                                                                                                   [100%]

================================================================== 5 passed in 0.01s ==================================================================

Using Docker

cd demo-interview-question-merge-intervals/
docker build -f Dockerfile.python . -t stefansavev/python_merge_intervals

To run:

docker run -it stefansavev/python_merge_intervals:latest

Implementation Details (Algorithm)

The following algorithm is used:

1. Sort the intervals by their start time.
2. Loop over the sorted intervals.

• Invariant: current is an interval that can grow from the end (but not from the start).
• a. If current is not set, set it to the interval from the loop iteration
• b1. If current is set and the interval from the loop can be merged to current, then grow/update current to a merged interval
• b2. If current is set but the loop interval does not overlap with current write current to output.
• c. Begin a new current interval

3. Make sure to output current interval

Testing

I use table driven tests with pytest.

Time to Completion

• 10 min for creating repository, setting up ssh keys, cloning
• 20 min for solving the merge intervals
• 20 min for code re-organization and pytest
• 40 min for code formatting, writing comments and README
• 20 min for Docker

Extra: Using GoLang

Build:

cd demo-interview-question-merge-intervals/
docker build -f Dockerfile.go . -t stefansavev/go_merge_intervals

Then run:

docker run -it stefansavev/go_merge_intervals:latest

Long story short

Simply run:

make

Requires Make and Docker.

Output of make

docker build -f Dockerfile.python . -t stefansavev/python_merge_intervals
Sending build context to Docker daemon  200.2kB
Step 1/7 : FROM python:3.9.0-slim-buster
 ---> 8842fc1a4cb7
Step 2/7 : RUN mkdir /app && pip install pytest
 ---> Using cache
 ---> fdf9f40f4d24
Step 3/7 : WORKDIR /app
 ---> Using cache
 ---> ff1c024c5aee
Step 4/7 : COPY python_merge_intervals/ python_merge_intervals/
 ---> Using cache
 ---> 94f63828dd1f
Step 5/7 : ENV PYTHONPATH=/app/
 ---> Using cache
 ---> 09197b42e07a
Step 6/7 : RUN cd python_merge_intervals && pytest .
 ---> Using cache
 ---> 76e77af2bbc1
Step 7/7 : CMD python python_merge_intervals/demo.py
 ---> Using cache
 ---> 254f1406b325
Successfully built 254f1406b325
Successfully tagged stefansavev/python_merge_intervals:latest
docker run -it stefansavev/python_merge_intervals:latest
[(2, 23), (25, 30)]
docker build -f Dockerfile.go . -t stefansavev/go_merge_intervals
Sending build context to Docker daemon  200.2kB
Step 1/7 : FROM golang:1.15.3-buster
 ---> 4a581cd6feb1
Step 2/7 : RUN mkdir /app && go get github.com/google/go-cmp/cmp
 ---> Using cache
 ---> eec130f41ea5
Step 3/7 : WORKDIR /app
 ---> Using cache
 ---> 3407a1a23f10
Step 4/7 : COPY golang_merge_intervals/ golang_merge_intervals/
 ---> Using cache
 ---> a82c08a08444
Step 5/7 : RUN cd golang_merge_intervals/merge_intervals && go test
 ---> Using cache
 ---> ab4c38df4d21
Step 6/7 : RUN cd golang_merge_intervals/main && go build demo.go
 ---> Using cache
 ---> 2448d2d5ec66
Step 7/7 : CMD golang_merge_intervals/main/demo
 ---> Using cache
 ---> 5e0b95f089ea
Successfully built 5e0b95f089ea
Successfully tagged stefansavev/go_merge_intervals:latest
docker run -it stefansavev/go_merge_intervals:latest
Output: [{"Start":2,"End":23},{"Start":25,"End":30}]