Tree Traversal Inorder Left Root Right in DSA C# - Build from Scratch

Tree Traversal Inorder Left Root Right

📖 Scenario: Imagine you have a family tree and you want to visit each family member in a special order: first the left child, then the parent, and finally the right child. This is called inorder traversal.

🎯 Goal: You will build a simple binary tree and write code to visit its nodes in inorder (left, root, right) order, then print the values.

📋 What You'll Learn

Create a binary tree with nodes having integer values

Add a helper variable to hold the traversal result

Write a recursive method to perform inorder traversal (left, root, right)

Print the traversal result as a list of node values

💡 Why This Matters

🌍 Real World

Tree traversal is used in many applications like searching files in folders, organizing data, and parsing expressions.

💼 Career

Understanding tree traversal is important for software developers working with data structures, databases, and algorithms.

1

Create the binary tree nodes

Create a class called Node with an integer Value and two Node references called Left and Right. Then create a root node with value 1, set its left child to a node with value 2, and its right child to a node with value 3.

DSA C#

// Define Node class and create root with left and right children
// Your code here

Hint

Define the Node class with a constructor. Then create root and assign its Left and Right properties.

2

Create a list to hold traversal results

Create a List<int> called result to store the values of nodes visited during inorder traversal.

DSA C#

public class Node
{
    public int Value;
    public Node Left;
    public Node Right;

    public Node(int value)
    {
        Value = value;
        Left = null;
        Right = null;
    }
}

Node root = new Node(1);
root.Left = new Node(2);
root.Right = new Node(3);

// Create a list called result to hold traversal values
// Your code here

Hint

Use List<int> from System.Collections.Generic to store values.

3

Write the inorder traversal method

Write a recursive method called InorderTraversal that takes a Node parameter called node. It should visit the left child first by calling itself with node.Left, then add node.Value to the result list, then visit the right child by calling itself with node.Right. Make sure to check if node is not null before visiting.

DSA C#

using System.Collections.Generic;

public class Node
{
    public int Value;
    public Node Left;
    public Node Right;

    public Node(int value)
    {
        Value = value;
        Left = null;
        Right = null;
    }
}

Node root = new Node(1);
root.Left = new Node(2);
root.Right = new Node(3);

List result = new List();

// Write the recursive InorderTraversal method below
// Your code here

Hint

Use recursion to visit left child, then current node, then right child. Add values to result.

4

Print the inorder traversal result

Print the result list as a comma-separated string using string.Join.

DSA C#

using System.Collections.Generic;
using System;

public class Node
{
    public int Value;
    public Node Left;
    public Node Right;

    public Node(int value)
    {
        Value = value;
        Left = null;
        Right = null;
    }
}

Node root = new Node(1);
root.Left = new Node(2);
root.Right = new Node(3);

List result = new List();

void InorderTraversal(Node node)
{
    if (node == null) return;
    InorderTraversal(node.Left);
    result.Add(node.Value);
    InorderTraversal(node.Right);
}

InorderTraversal(root);

// Print the result list as comma separated values
// Your code here

Hint

Use Console.WriteLine(string.Join(",", result)) to print the values separated by commas.

Practice

1. What is the order of nodes visited in an inorder traversal of a binary tree?

easy

A. Left subtree, Root, Right subtree

B. Root, Left subtree, Right subtree

C. Right subtree, Root, Left subtree

D. Root, Right subtree, Left subtree

Solution

1. Step 1: Understand inorder traversal definition

   Inorder traversal means visiting the left subtree first, then the root node, and finally the right subtree.

2. Step 2: Apply the order to the tree nodes

   This order ensures nodes are visited in ascending order for binary search trees.

3. Final Answer:

   Left subtree, Root, Right subtree -> Option A

4. Quick Check:

   Inorder = Left, Root, Right [OK]

Hint: Remember: Inorder = Left, Root, Right [OK]

Common Mistakes:

• Confusing inorder with preorder or postorder
• Visiting root before left subtree
• Visiting right subtree before root

2. Which of the following C# method signatures correctly represents an inorder traversal method for a binary tree node class named Node?

easy

A. void InorderTraversal(Node root)

B. int InorderTraversal(Node root)

C. Node InorderTraversal()

D. bool InorderTraversal(Node root)

Solution

1. Step 1: Identify the purpose of the method

   An inorder traversal method typically visits nodes and prints or processes them without returning a value, so it should be void.

2. Step 2: Check method signature options

   void InorderTraversal(Node root) uses void return type and accepts a Node parameter, which is correct for traversal.

3. Final Answer:

   void InorderTraversal(Node root) -> Option A

4. Quick Check:

   Traversal methods usually return void [OK]

Hint: Traversal methods usually return void [OK]

Common Mistakes:

• Using return types like int or bool unnecessarily
• Missing the root parameter
• Returning Node instead of void

3. Given the following binary tree:

    2
   / \
  1   3

What is the output of the inorder traversal method that prints node values?

medium

A. 1 3 2

B. 2 1 3

C. 3 2 1

D. 1 2 3

Solution

1. Step 1: Apply inorder traversal on the tree

   Visit left subtree (1), then root (2), then right subtree (3).

2. Step 2: Write the visited nodes in order

   The nodes are visited in order: 1, 2, 3.

3. Final Answer:

   1 2 3 -> Option D

4. Quick Check:

   Inorder traversal output = 1 2 3 [OK]

Hint: Inorder prints nodes in ascending order for BST [OK]

Common Mistakes:

• Printing root before left subtree
• Swapping left and right subtree order
• Confusing with preorder or postorder output

4. Consider this C# inorder traversal method:

void InorderTraversal(Node root) {
    if (root == null) return;
    InorderTraversal(root.Right);
    Console.Write(root.Value + " ");
    InorderTraversal(root.Left);
}

What is the error in this code?

medium

A. It causes infinite recursion

B. It misses the base case for null root

C. It visits right subtree before left subtree, reversing inorder order

D. It does not print the root value

Solution

1. Step 1: Analyze the traversal order in the code

   The code visits root.Right first, then root, then root.Left, which is reverse of inorder.

2. Step 2: Identify the correct inorder order

   Inorder should visit left subtree first, then root, then right subtree.

3. Final Answer:

   It visits right subtree before left subtree, reversing inorder order -> Option C

4. Quick Check:

   Inorder = Left, Root, Right [OK]

Hint: Inorder must visit left subtree before right [OK]

Common Mistakes:

• Swapping left and right subtree calls
• Forgetting to check for null root
• Not printing root value

5. You have a binary tree where each node contains an integer. You want to collect all node values in a list using inorder traversal. Which C# code snippet correctly implements this?

hard

A. void Inorder(Node root, List<int> result) {
if (root == null) return;
result.Add(root.Value);
Inorder(root.Left, result);
Inorder(root.Right, result);
}

B. void Inorder(Node root, List<int> result) {
if (root == null) return;
Inorder(root.Left, result);
result.Add(root.Value);
Inorder(root.Right, result);
}

C. void Inorder(Node root, List<int> result) {
if (root == null) return;
Inorder(root.Right, result);
result.Add(root.Value);
Inorder(root.Left, result);
}

D. void Inorder(Node root, List<int> result) {
if (root == null) return;
Inorder(root.Left, result);
Inorder(root.Right, result);
result.Add(root.Value);
}

Solution

1. Step 1: Recall inorder traversal order

   Inorder visits left subtree, then root, then right subtree.

2. Step 2: Check which code matches this order

   void Inorder(Node root, List<int> result) { if (root == null) return; Inorder(root.Left, result); result.Add(root.Value); Inorder(root.Right, result); } visits left subtree, adds root value, then visits right subtree, correctly collecting values in order.

3. Final Answer:

   void Inorder(Node root, List<int> result) { if (root == null) return; Inorder(root.Left, result); result.Add(root.Value); Inorder(root.Right, result); } -> Option B

4. Quick Check:

   Left, Root, Right order with result.Add(root.Value) in middle [OK]

Hint: Add root value between left and right recursive calls [OK]

Common Mistakes:

• Adding root value before left subtree
• Adding root value after right subtree
• Swapping left and right subtree calls