https://stackoverflow.com/questions/13212212/creating-two-dimensional-arrays-in-rust
https://pcwalton.github.io/2013/03/18/an-overview-of-memory-management-in-rust.html
https://doc.rust-lang.org/alloc/string/struct.String.html
https://doc.rust-lang.org/book/ch08-03-hash-maps.html