Left Side View of Binary Tree in DSA Javascript - Build from Scratch

Left Side View of Binary Tree

📖 Scenario: Imagine you have a family tree represented as a binary tree. You want to see only the leftmost family members at each generation level.

🎯 Goal: Build a program that finds the left side view of a binary tree, showing the first node visible at each level from the left side.

📋 What You'll Learn

Create a binary tree using nodes with val, left, and right properties

Use a variable to keep track of the current level during traversal

Implement a function to collect the leftmost nodes at each level

Print the array of left side view node values

💡 Why This Matters

🌍 Real World

Left side view of a binary tree helps in visualizing hierarchical data from a specific perspective, useful in family trees, organizational charts, and decision trees.

💼 Career

Understanding tree traversal and views is important for software engineers working with hierarchical data structures, UI rendering, and algorithms.

1

Create the Binary Tree

Create a binary tree with a root node called root having value 1. Its left child should have value 2 and right child should have value 3. The left child of node 2 should have value 4, and the right child of node 3 should have value 5.

DSA Javascript

// Create the binary tree nodes and link them
// Your code here

Hint

Use objects with val, left, and right properties to build the tree.

2

Set Up Level Tracking Variable

Create an empty array called leftView to store the left side view node values.

DSA Javascript

const root = {
  val: 1,
  left: {
    val: 2,
    left: { val: 4, left: null, right: null },
    right: null
  },
  right: {
    val: 3,
    left: null,
    right: { val: 5, left: null, right: null }
  }
};

// Create an empty array called leftView
// Your code here

Hint

Use const leftView = []; to create an empty array.

3

Implement Left Side View Function

Write a function called leftSideView that takes node and level as parameters. If node is null, return immediately. If level is equal to the length of leftView, push node.val into leftView. Then recursively call leftSideView for the left child with level + 1, followed by the right child with level + 1. Finally, call leftSideView with root and 0.

DSA Javascript

const root = {
  val: 1,
  left: {
    val: 2,
    left: { val: 4, left: null, right: null },
    right: null
  },
  right: {
    val: 3,
    left: null,
    right: { val: 5, left: null, right: null }
  }
};

const leftView = [];

// Write the leftSideView function and call it with root and 0
// Your code here

Hint

Use recursion to visit nodes level by level, adding the first node at each level to leftView.

4

Print the Left Side View

Print the leftView array using console.log(leftView).

DSA Javascript

const root = {
  val: 1,
  left: {
    val: 2,
    left: { val: 4, left: null, right: null },
    right: null
  },
  right: {
    val: 3,
    left: null,
    right: { val: 5, left: null, right: null }
  }
};

const leftView = [];

function leftSideView(node, level) {
  if (node === null) return;
  if (level === leftView.length) {
    leftView.push(node.val);
  }
  leftSideView(node.left, level + 1);
  leftSideView(node.right, level + 1);
}

leftSideView(root, 0);

// Print the leftView array
// Your code here

Hint

Use console.log(leftView) to see the left side view array.