Breadth-first traversal

Question

I was trying to solve one interview question, but for that I have to travel the binary tree level by level. I have designed BinaryNode with having below variable

Answer 1

A breadth first search is usually implemented with a queue, a depth first search using a stack.

Queue q = new Queue();
q.Enqueue(root);
while(q.Count > 0)
{
    Node current = q.Dequeue();
    if(current == null)
        continue;
    q.Enqueue(current.Left);
    q.Enqueue(current.Right);

    DoSomething(current);
}

As an alternative to checking for null after dequeuing you can check before adding to the Queue. I didn't compile the code, so it might contain some small mistakes.

---

A fancier (but slower) version that integrates well with LINQ:

public static IEnumerable BreadthFirstTopDownTraversal(T root, Func> children)
{
    var q = new Queue();
    q.Enqueue(root);
    while (q.Count > 0)
    {
        T current = q.Dequeue();
        yield return current;
        foreach (var child in children(current))
            q.Enqueue(child);
    }
}

Which can be used together with a Children property on Node:

IEnumerable Children { get { return new []{ Left, Right }.Where(x => x != null); } }

...

foreach(var node in BreadthFirstTopDownTraversal(root, node => node.Children))
{
   ...
}