Left Side View of Binary Tree in DSA Javascript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Left Side View for a Simple Binary Tree

What is the output of the following code that prints the left side view of a binary tree?

DSA Javascript

class Node {
  constructor(val) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

function leftSideView(root) {
  const result = [];
  function dfs(node, level) {
    if (!node) return;
    if (level === result.length) {
      result.push(node.val);
    }
    dfs(node.left, level + 1);
    dfs(node.right, level + 1);
  }
  dfs(root, 0);
  return result;
}

const root = new Node(1);
root.left = new Node(2);
root.right = new Node(3);
root.left.right = new Node(5);
root.right.right = new Node(4);

console.log(leftSideView(root));

A [1, 3, 5]

B [1, 3, 4]

C [1, 2, 5]

D [1, 2, 4]

💡 Hint

Think about which nodes are visible when looking from the left side, level by level.

The left side view includes the first node encountered at each level when traversing left to right. At level 0: 1, level 1: 2, level 2: 5.

❓ Predict Output

intermediate

Left Side View Output for a Skewed Tree

What will be the output of the leftSideView function for this skewed binary tree?

DSA Javascript

class Node {
  constructor(val) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

function leftSideView(root) {
  const result = [];
  function dfs(node, level) {
    if (!node) return;
    if (level === result.length) {
      result.push(node.val);
    }
    dfs(node.left, level + 1);
    dfs(node.right, level + 1);
  }
  dfs(root, 0);
  return result;
}

const root = new Node(10);
root.left = new Node(20);
root.left.left = new Node(30);
root.left.left.left = new Node(40);

console.log(leftSideView(root));

A [10, 20, 30, 40]

B [10, 20, 30]

C [10, 30, 40]

D [10, 20, 40]

💡 Hint

Since the tree is skewed to the left, all nodes should be visible from the left side.

Each level has only one node on the left side, so the output includes all nodes in the left chain.

🔧 Debug

advanced

Identify the Bug in Left Side View Implementation

The following code is intended to return the left side view of a binary tree. What is the bug causing incorrect output?

DSA Javascript

function leftSideView(root) {
  const result = [];
  function dfs(node, level) {
    if (!node) return;
    dfs(node.left, level + 1);
    dfs(node.right, level + 1);
    if (level === result.length) {
      result.push(node.val);
    }
  }
  dfs(root, 0);
  return result;
}

A The check for adding node.val to result is after recursive calls, causing right nodes to be added first.

B The base case is missing, so the function runs infinitely.

C The function uses BFS instead of DFS, which is incorrect for left side view.

D The result array is not initialized before recursion.

💡 Hint

Think about when nodes are added to the result relative to recursion order.

Adding nodes after recursion causes right nodes to be added before left nodes at the same level, breaking the left side view logic.

🧠 Conceptual

advanced

Understanding Left Side View with BFS

Which statement correctly describes how to get the left side view of a binary tree using breadth-first search (BFS)?

A Add nodes only if they have a left child.

B At each level, add the last node encountered in the queue to the result list.

C Add all nodes at each level to the result list.

D At each level, add the first node encountered in the queue to the result list.

💡 Hint

Think about which node is visible from the left side at each level.

In BFS, nodes are processed level by level from left to right, so the first node at each level is the leftmost visible node.

🚀 Application

expert

Left Side View with Missing Left Children

Given the binary tree below, what is the left side view output? Tree structure: - Root: 7 - Root.right: 9 - Root.right.left: 8 - Root.right.right: 10 Use the standard left side view logic (first node at each level from left to right).

A [7, 8, 10]

B [7, 9, 8]

C [7, 9, 10]

D [7, 8]

💡 Hint

Even if left child is missing, the first node at each level from left to right is included.

Level 0: 7, level 1: 9 (only right child), level 2: 8 (left child of 9) is first at that level.