Level-Order Traversal

Visit a tree breadth-first with a queue.

Algorithm

The canonical tree is 4(2(1,3),6(5,7)), so this C# DSA implementation can be compared directly with the rest of the DSA track.

Basic Implementation

basic.cs

using System;
using System.Collections.Generic;
using System.Linq;

class Node {
    public int Value;
    public Node? Left;
    public Node? Right;
    public Node(int value, Node? left = null, Node? right = null) { Value = value; Left = left; Right = right; }
}
class Program {
    static string Render(Node? node) {
        if (node == null) return "_";
        if (node.Left == null && node.Right == null) return node.Value.ToString();
        return $"{node.Value}({Render(node.Left)},{Render(node.Right)})";
    }
    static Node SampleTree() => new Node(4, new Node(2, new Node(1), new Node(3)), new Node(6, new Node(5), new Node(7)));
    static string ListString(IEnumerable<int> values) => "[" + string.Join(", ", values) + "]";
    static void Main() { var queue = new Queue<Node>(); queue.Enqueue(SampleTree()); var output = new List<int>(); while (queue.Count > 0) { var node = queue.Dequeue(); output.Add(node.Value); if (node.Left != null) queue.Enqueue(node.Left); if (node.Right != null) queue.Enqueue(node.Right); } Console.WriteLine(ListString(output)); }
}

Complexity

Time: O(n)
Space: O(w) queue space

Implementation notes

Render tree structure explicitly instead of printing node objects.
The replay highlights the node, traversal state, queue, path, or search cursor that changes at each step.

level order Level-order traversal uses a queue to visit shallower nodes first.