For perspective, I'm a novice with algorithm design, I've been grinding leetcode for the past 6 months or so, almost exclusively in Rust. I was bewildered by th

For perspective, I'm a novice with algorithm design, I've been grinding leetcode for the past 6 months or so, almost exclusively in Rust. I was bewildered by the same concern since I had initially set out to, not only focus on Rust, but to primarily maximize use of the Iterator construct, since I was not intricately familiar with it. A few months in I discovered that there was an appropriate Iterator construct which accomplishes the same thing. // Comments for the non-Rust native reader, regarding this Function declaration: // successors is a function that accepts an `Option` container for some Value of type T, called `first` // and a Closure called `succ`, constrained below: pub fn successors<T, F>(first: Option<T>, succ: F) -> Successors<T, F> ⓘ where // `succ` must receive the iterated state, and return the next iterated state F: FnMut(&T) -> Option<T>, // Each time the `next()` function is called on the returned Iterator (a Successors-flavored iterator), // the state of `first` is yielded, and then // `succ` is called to progress // until a `None` type is reported by `succ` I'm not sure where the concept came from, but it's not dissimilar to the author's implementation, but instead of the ControlFlow enum, it relies simply on the Option enum. I know though, that it was initially built in the Itertools crate as unfold and then upstreamed some time later. Essentially you use `first` to contain a Queue, Stack, or Level for the different traversals, and define traversal or activities from there. It's fairly ergonomic in practice, ergonomic enough for Leetcode. Here's a BFS: https://leetcode.com/problems/course-schedule-iv/solutions/6297286/functional-iterator-approach-with-successors-2ms/ https://leetcode.com/problems/course-schedule-iv/solutions/6... [0] https://doc.rust-lang.org/std/iter/fn.successors.html https://doc.rust-lang.org/std/iter/fn.successors.html [1] https://docs.rs/itertools/latest/itertools/fn.unfold.html https://docs.rs/itertools/latest/itertools/fn.unfold.html