N26 Backend Challenge

API to store and get statistics of last 60 seconds of transactions.

How to run

1. Install Maven locally
2. Run: mvn clean install
3. Run: cd target
4. Run: java -jar challenge-0.0.1.jar
5. You can turn on debug output by changing the debug level in application.properties file to DEBUG

Adding transactions

Run the following in your terminal:

curl -d '{"amount":1, "timestamp":1478192204000}' -H "Content-Type: application/json" -X POST -i localhost:8080/transactions

If you don't have curl, then use postman to send a POST request to localhost:8080/transactions with a valid json in body. Containing amount and timestamp of transaction. Make sure you change the timestamp number to the current Unix epoch timestamp.

Getting statistics

The following will give you statistics about all transactions in the last 60 seconds:

curl -i localhost:8080/statistics

You can also use a browser and go to localhost:8080/statistics to get statistics of last 60 seconds of transactions

Description:

This is a Spring boot based Java web project. It accepts transaction via a POST endpoint and give statistics via GET endpoint as JSON.

Both endpoints have a complexity of O(1).

This is done by storing data in a fixed size array, where the indexes are a modulus of the timestamps. Depending on the time the statistics endpoint is called, output data contains transactions with a varying maximum age between under 59 and under 60 seconds.

The transactions endpoint, which receives transactions via POST, always uses appr. 8 arithmetic operations. It's speed and performance is completely independent from how many transactions are being sent.