Left Side View of Binary Tree in DSA C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Left Side View of a Binary Tree?

The Left Side View of a Binary Tree is the set of nodes visible when the tree is viewed from the left side. It includes the leftmost node at each level of the tree.

beginner

Which tree traversal method is commonly used to find the Left Side View of a Binary Tree?

Level Order Traversal (Breadth-First Search) is commonly used. We visit nodes level by level and pick the first node at each level to form the left side view.

beginner

In the Left Side View algorithm, why do we pick the first node at each level?

Because the first node visited at each level during level order traversal is the leftmost node visible from the left side.

beginner

What data structure is typically used to implement the Left Side View algorithm?

A queue is used to perform level order traversal, which helps process nodes level by level.

beginner

How does the Left Side View differ from the Right Side View of a Binary Tree?

The Left Side View shows the leftmost nodes at each level, while the Right Side View shows the rightmost nodes at each level when viewed from the right side.

What node do you add to the left side view list at each level during traversal?

A The middle node at that level

B The last node visited at that level

C The first node visited at that level

D All nodes at that level

The first node visited at each level during level order traversal is the leftmost node visible from the left side.

Which data structure helps in level order traversal for the left side view?

A Queue

B Stack

C Hash Map

D Linked List

A queue is used to process nodes level by level in level order traversal.

If a binary tree has only right children, what will the left side view contain?

A Only the root node

B Only leaf nodes

C No nodes

D All nodes in the tree

Since each level has only one node (the right child), that node is also the leftmost node at that level.

What traversal order is NOT typically used to find the left side view?

A Level Order Traversal

B Preorder Traversal

C Breadth-First Search

D Queue-based traversal

Preorder traversal is depth-first and does not guarantee visiting the leftmost node first at each level.

What is the time complexity of finding the left side view of a binary tree using level order traversal?

A O(n)

B O(log n)

C O(n^2)

D O(1)

Each node is visited once, so the time complexity is linear, O(n), where n is the number of nodes.

Explain how to find the Left Side View of a Binary Tree using level order traversal.

Think about how you see the tree from the left side and which nodes are visible.

Describe the difference between Left Side View and Right Side View of a Binary Tree.

Imagine standing on the left or right side of the tree.

Practice

1. What does the "Left Side View" of a binary tree represent?

easy

A. Nodes at the deepest level of the tree

B. Nodes visible when the tree is viewed from the right side

C. All leaf nodes of the tree

D. Nodes visible when the tree is viewed from the left side

Solution

1. Step 1: Understand the view perspective

   The left side view shows nodes visible when looking at the tree from the left side.

2. Step 2: Identify visible nodes

   Only the first node encountered at each level from the left is visible in this view.

3. Final Answer:

   Nodes visible when the tree is viewed from the left side -> Option D

4. Quick Check:

   Left side view = nodes visible from left [OK]

Hint: Left side view shows first node at each level from left [OK]

Common Mistakes:

• Confusing left side view with right side view
• Thinking it shows all leaf nodes
• Assuming it shows deepest nodes only

2. Which of the following C++ code snippets correctly declares a node structure for a binary tree used in left side view traversal?

easy

A. struct Node { int data; Node* left; Node* right; };

B. struct Node { int data; Node left; Node right; };

C. struct Node { int data; Node* left; int right; };

D. struct Node { int data; int left; int right; };

Solution

1. Step 1: Check pointer usage for child nodes

   Child nodes must be pointers to allow dynamic linking in a tree.

2. Step 2: Validate data types

   Data is int, left and right children are pointers to Node, matching correct binary tree node structure.

3. Final Answer:

   struct Node { int data; Node* left; Node* right; }; -> Option A

4. Quick Check:

   Use pointers for child nodes in tree struct [OK]

Hint: Use pointers for left and right child nodes in struct [OK]

Common Mistakes:

• Using Node instead of Node* for children
• Using int type for child nodes
• Omitting pointers causing infinite size error

3. Consider the following binary tree:

      1
     / \
    2   3
   / \   \
  4   5   6

What is the left side view output of this tree?

medium

A. [1, 3, 6]

B. [1, 2, 4]

C. [1, 2, 5]

D. [1, 2, 6]

Solution

1. Step 1: Identify nodes visible from left at each level

   Level 1: 1, Level 2: 2 (left child), Level 3: 4 (left child of 2)

2. Step 2: Collect nodes in order

   Left side view nodes are [1, 2, 4]

3. Final Answer:

   [1, 2, 4] -> Option B

4. Quick Check:

   Left side view nodes = [1, 2, 4] [OK]

Hint: Pick first node at each level from left [OK]

Common Mistakes:

• Choosing right child nodes instead of left
• Including nodes not visible from left
• Mixing nodes from different levels

4. The following C++ function is intended to print the left side view of a binary tree. What is the error?

void leftViewUtil(Node* root, int level, int &maxLevel) {
    if (!root) return;
    if (level > maxLevel) {
        cout << root->data << " ";
        maxLevel = level;
    }
    leftViewUtil(root->left, level + 1, maxLevel);
    leftViewUtil(root->right, level + 1, maxLevel);
}

void leftView(Node* root) {
    int maxLevel = 0;
    leftViewUtil(root, 1, maxLevel);
}

medium

A. The order of recursive calls should be right child first, then left child

B. maxLevel should be initialized to -1 instead of 0

C. No error; function correctly prints left side view

D. The function should print after both recursive calls

Solution

1. Step 1: Analyze traversal order and maxLevel usage

   The function visits left child first, then right child, printing first node at each level.

2. Step 2: Check initialization and printing logic

   maxLevel initialized to 0 and level starts at 1, so first level prints correctly; printing before recursion is correct.

3. Final Answer:

   No error; function correctly prints left side view -> Option C

4. Quick Check:

   Correct preorder traversal prints left view [OK]

Hint: Left child first recursion prints left view correctly [OK]

Common Mistakes:

• Changing recursion order breaks left view logic
• Incorrect maxLevel initialization causing missed nodes
• Printing after recursion misses first nodes

5. Given a binary tree where some levels have missing left children but have right children, which approach ensures correct left side view output?

hard

A. Traverse level order and pick first node at each level

B. Traverse preorder and print nodes only if left child exists

C. Traverse inorder and print nodes at odd levels

D. Traverse postorder and print leaf nodes only

Solution

1. Step 1: Understand problem with missing left children

   Left side view must include visible nodes even if left child is missing but right child exists.

2. Step 2: Choose traversal that captures first visible node per level

   Level order traversal visits nodes level by level, so picking first node at each level ensures correct left side view.

3. Final Answer:

   Traverse level order and pick first node at each level -> Option A

4. Quick Check:

   Level order first node per level = left side view [OK]

Hint: Use level order traversal, pick first node at each level [OK]

Common Mistakes:

• Ignoring right child when left child is missing
• Using preorder which may miss visible nodes
• Confusing inorder or postorder with left view logic