BST vs Hash Map Trade-offs for Ordered Data in DSA Javascript - Compare & Choose

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why choose a BST over a Hash Map for ordered data?

Which of the following is the main reason to prefer a Binary Search Tree (BST) instead of a Hash Map when you need to keep data in order?

A BST keeps data sorted and allows in-order traversal to get ordered data easily.

B BST uses less memory than Hash Map in all cases.

C BST has faster average lookup time than Hash Map.

D BST automatically handles duplicate keys better than Hash Map.

💡 Hint

Think about how you get sorted data from each structure.

BST stores data in a way that allows in-order traversal to retrieve sorted data. Hash Maps do not maintain order.

❓ Predict Output

intermediate

Output of in-order traversal on BST

What is the output of the in-order traversal of this BST?

DSA Javascript

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

function inorder(root, result = []) {
  if (!root) return result;
  inorder(root.left, result);
  result.push(root.val);
  inorder(root.right, result);
  return result;
}

// Construct BST
const root = new Node(10);
root.left = new Node(5);
root.right = new Node(15);
root.left.left = new Node(3);
root.left.right = new Node(7);
root.right.right = new Node(18);

console.log(inorder(root));

A [18, 15, 10, 7, 5, 3]

B [10, 5, 3, 7, 15, 18]

C [3, 5, 7, 10, 15, 18]

D [5, 3, 7, 10, 15, 18]

💡 Hint

In-order traversal visits left subtree, node, then right subtree.

In-order traversal of BST visits nodes in ascending order.

❓ Predict Output

advanced

Hash Map key order after insertions

What will be the order of keys when iterating over this JavaScript Map?

DSA Javascript

const map = new Map();
map.set('b', 2);
map.set('a', 1);
map.set('c', 3);

const keys = [];
for (const key of map.keys()) {
  keys.push(key);
}
console.log(keys);

A []

B ["b", "a", "c"]

C ["c", "b", "a"]

D ["a", "b", "c"]

💡 Hint

JavaScript Map preserves insertion order of keys.

Map keys are iterated in the order they were added.

🧠 Conceptual

advanced

Time complexity trade-offs between BST and Hash Map

Which statement correctly compares average time complexities of search operations in a balanced BST and a Hash Map?

A Balanced BST search is O(log n), Hash Map search is O(1) on average.

B Balanced BST search is O(n), Hash Map search is O(log n) on average.

C Balanced BST search is O(1), Hash Map search is O(log n) on average.

D Both Balanced BST and Hash Map have O(n) search time on average.

💡 Hint

Think about how balanced trees and hash maps organize data.

Balanced BSTs have logarithmic search time; Hash Maps have constant average search time.

🚀 Application

expert

Choosing data structure for range queries on ordered data

You need to store a large set of numbers and frequently perform range queries (e.g., find all numbers between 10 and 50). Which data structure is best suited for this task?

A Stack, because it allows easy access to the last inserted number.

B Hash Map, because it provides constant time lookups for any number.

C Unsorted Array, because it uses less memory and is faster for insertions.

D Balanced Binary Search Tree, because it supports efficient range queries via in-order traversal.

💡 Hint

Consider which structure allows ordered traversal and efficient range filtering.

Balanced BSTs keep data sorted and allow efficient range queries by traversing only relevant parts.