Arrays can be concatnated with Array#concat method but there is no built-in function to concatnating sorted arrays with giving a certain order
In Rust, iterable objects have peek method to get the next value without advancing the iterator.
[Peekable in std::iter - Rust](https://doc.rust-lang.org/stable/std/iter/struct.Peekable.html)
This concept could be used to achieve the purpose.
In merging 2 arrays with giving a certain order, peek