Exchange Rate

The best Exchange Rate path search for a given set of Exchanges, Currencies, Exchange Rates and Exchange Rate Requests.

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Overview

In order to provide customers a product that lets them spend cryptocurrencies to buy goods from merchants who only accept fiat currency, we need to solve two problems: 1. Determine a sequence of trades and transfers across exchanges to convert the cryptocurrency to fiat currency with a suitable exchange rate. 2. Provide the best possible exchange rate to customers.

The idea is based on the challenge I received once as a part of an interview.

Build and Run the code

As a standard Rust project, building it and running it is what you would expect.

Build

cargo build or cargo build --release

Run

cargo run < data/exchange-rate-path-input.txt or cargo run --release < data/exchange-rate-path-input.txt

Input format

Input is formed by two types of lines: "Price Update" and "Exchange Rate Request". Example of the expected input format can be found in data/exchange-rate-input.txt.

Price Update

• Format: <timestamp> <exchange> <source_currency> <destination_currency> <forward_factor> <backward_factor>
• Example: 2019-08-01T08:42:22+00:00 BITFINEX BTC USD 1000.0 0.0009

Exchange Rate Request

• Format: EXCHANGE_RATE_REQUEST <source_exchange> <source_currency> <destination_exchange> <destination_currency>
• Example: EXCHANGE_RATE_REQUEST BITFINEX ETH BINANCE BTC

Design

The implementation consist from three main parts and a gel connecting them together.

1.) Graph

I decided not to use Petgraph create (petgraph) directly, but ruther to extract and refactor GraphMap into my own crate called Safe Graph (safe-graph). My reasing for that is explained there.

2.) Floyd-Warshall algorithm

A generic solution for Floyd-Warshall algorithm supporting customization is provided by my own crate Floyd Warshall algorithm (floyd-warshall-alg). Available customization is described there.

3.) IO - reading Request, processing it and writing Response

Input: Reading and parsing input from stdin to Request instance holding instances of PriceUpdate and ExchangeRateRequest structs.

Processing: Constructing a graph, running a customized version of Floyd-Warshall algorithm and forming a Response.

Output: Writing the Response holding instances of BestRatePath struct to stdout.

License

Licensed under the General Public License (GPL), version 3 (LICENSE http://www.gnu.org/licenses/gpl-3.0.en.html).