Breath first traversal

Tree/Forest/Node may provide bfs()/bfs_mut()/into_bfs(), which iterate all its child nodes in the manner of breadth first search. Note that not all data structures provide all three kinds of iterators.

During breadth first search, you can get:

1. data associated with Node.

2. size info -- degree and node count.

Example of BFS iteration

#![allow(unused)]
fn main() {
use trees::{Size, bfs, tr};

let tree = tr(0) /( tr(1)/tr(2)/tr(3) ) /( tr(4)/tr(5)/tr(6) );
let visits = tree.into_bfs().iter.collect::<Vec<_>>();
assert_eq!( visits, vec![
    bfs::Visit{ data: 0, size: Size{ degree: 2, descendants: 6 }},
    bfs::Visit{ data: 1, size: Size{ degree: 2, descendants: 2 }},
    bfs::Visit{ data: 4, size: Size{ degree: 2, descendants: 2 }},
    bfs::Visit{ data: 2, size: Size{ degree: 0, descendants: 0 }},
    bfs::Visit{ data: 3, size: Size{ degree: 0, descendants: 0 }},
    bfs::Visit{ data: 5, size: Size{ degree: 0, descendants: 0 }},
    bfs::Visit{ data: 6, size: Size{ degree: 0, descendants: 0 }},
]);
}

Trees can be constructed from and converted into an owning BFS iterator, making it a bridge for conversions between trees.

Example of collecting scattered nodes to piled ones

#![allow(unused)]
fn main() {
use trees::{Tree, tr};

let scattered_tree = tr(0) /( tr(1)/tr(2)/tr(3) ) /( tr(4)/tr(5)/tr(6) );
let piled_tree = Tree::<i32>::from( scattered_tree.into_bfs() );
}