Build a Binary Tree

Create a fixed seven-node binary tree and render its shape.

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() { Console.WriteLine(Render(SampleTree())); }
}

Complexity

Time: O(n)
Space: O(n)

Implementation notes

Render tree structure explicitly instead of printing node objects.
Node is a class, so each new Node(...) creates a managed reference object owned by the CLR and reclaimed by GC. The constructor defaults Node? left and Node? right to null, making absent children explicit in the object graph even when the canonical tree fills every leaf position in the render.
The replay highlights the node, traversal state, queue, path, or search cursor that changes at each step.

node links A node stores one value plus references to its left and right children.