BST Property and Why It Matters in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a value should go to the left subtree in a BST.

DSA Javascript

if (value [1] node.value) {
  // go left
}

Drag options to blanks, or click blank then click option'

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' causes wrong subtree choice.

Using '==' or '!=' is incorrect for BST placement.

In a BST, values less than the current node go to the left subtree.

2fill in blank

medium

Complete the code to insert a new value into the BST correctly.

DSA Javascript

if (value [1] node.value) {
  node.left = insert(node.left, value);
} else {
  node.right = insert(node.right, value);
}

Drag options to blanks, or click blank then click option'

A>

B<=

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' causes duplicates to go left, which may be incorrect depending on BST rules.

Using '==' is not suitable for comparison here.

Values less than the node go to the left subtree; others go right.

3fill in blank

hard

Fix the error in the BST search condition to find a value.

DSA Javascript

if (node.value [1] value) {
  return search(node.left, value);
} else if (node.value === value) {
  return node;
} else {
  return search(node.right, value);
}

Drag options to blanks, or click blank then click option'

A>

B<

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' causes searching the wrong subtree.

Using '<=' or '>=' can cause incorrect search paths.

If the node's value is greater than the target, search left subtree; else right.

4fill in blank

hard

Fill both blanks to create a BST property check function.

DSA Javascript

function isBST(node) {
  if (!node) return true;
  if (node.left && node.left.value [1] node.value) return false;
  if (node.right && node.right.value [2] node.value) return false;
  return isBST(node.left) && isBST(node.right);
}

Drag options to blanks, or click blank then click option'

A>=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' for left child check causes wrong validation.

Using '>=' for right child check causes wrong validation.

Left child must be less than node (so fail if left >= node). Right child must be greater than node (fail if right <= node).

5fill in blank

hard

Fill all three blanks to create a function that collects BST values in order.

DSA Javascript

function inorderTraversal(node, result = []) {
  if (!node) return result;
  inorderTraversal(node.[1], result);
  result.push(node.[2]);
  inorderTraversal(node.[3], result);
  return result;
}

Drag options to blanks, or click blank then click option'

Aleft

Bvalue

Cright

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'parent' instead of 'left' or 'right' causes errors.

Pushing node instead of node.value adds wrong data.

Inorder traversal visits left subtree, then node value, then right subtree.