Tree Traversal Inorder Left Root Right in DSA C# - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the order of nodes visited in an inorder tree traversal?

In inorder traversal, nodes are visited in the order: Left subtree, Root node, then Right subtree.

beginner

Why is inorder traversal useful for binary search trees (BST)?

Inorder traversal of a BST visits nodes in ascending sorted order, which helps in retrieving sorted data easily.

beginner

What is the base case in a recursive inorder traversal function?

The base case is when the current node is null, meaning there is no node to visit, so the function returns without action.

beginner

Show the inorder traversal output for this tree:
Root=2, Left=1, Right=3

The inorder traversal visits nodes in order: 1 -> 2 -> 3

beginner

What is the difference between inorder and preorder traversal?

Inorder visits nodes as Left, Root, Right. Preorder visits nodes as Root, Left, Right.

In inorder traversal, which node is visited first?

A Left child node

B Root node

C Right child node

D None of the above

In inorder traversal, the left subtree is visited first before the root.

What will be the inorder traversal output of a tree with nodes 4 (root), 2 (left), 5 (right)?

A 4 -> 2 -> 5

B 5 -> 4 -> 2

C 2 -> 4 -> 5

D 2 -> 5 -> 4

Inorder visits left subtree (2), root (4), then right subtree (5).

Which traversal method visits nodes in sorted order for a binary search tree?

A Inorder

B Preorder

C Postorder

D Level order

Inorder traversal visits BST nodes in ascending sorted order.

What is the first step in a recursive inorder traversal function?

A Visit the root node

B Return null

C Traverse the right subtree

D Traverse the left subtree

Inorder traversal starts by traversing the left subtree recursively.

If a node has no left child, what does inorder traversal do next?

A Traverse right subtree

B Visit the node itself

C Return immediately

D Skip the node

If no left child, inorder visits the current node before moving to right subtree.

Explain the steps of inorder traversal on a binary tree.

Think about the order Left, Root, Right.

Describe why inorder traversal is important for binary search trees.

Consider how BST properties relate to traversal order.

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