Validate if Tree is BST in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the current node is null.

DSA Typescript

if (root [1] null) return true;

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

A!==

B===

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '===' causes incorrect null check.

Using '>' or '<' operators for null comparison.

We check if root is exactly null to handle the base case of recursion.

2fill in blank

medium

Complete the code to check if the current node's value is within the valid range.

DSA Typescript

if (root.val [1] min || root.val [2] max) return false;

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

A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '>' instead of '<=' or '>=' causes boundary errors.

Checking only one side of the range.

The node's value must be strictly greater than min and strictly less than max, so we check if it is less than or equal to min or greater than or equal to max to return false.

3fill in blank

hard

Fix the error in the recursive call to validate left subtree with updated max.

DSA Typescript

return isValidBST(root.left, min, [1]) && isValidBST(root.right, root.val, max);

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

Aroot.val

Bmin

Cmax

Droot.left.val

Attempts:

3 left

💡 Hint

Common Mistakes

Passing min or max incorrectly causes wrong validation.

Using root.left.val instead of root.val.

For the left subtree, the maximum allowed value is the current node's value.

4fill in blank

hard

Fill both blanks to correctly validate the right subtree with updated min.

DSA Typescript

return isValidBST(root.left, min, root.val) && isValidBST(root.right, [1], [2]);

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

Aroot.val

Bmin

Cmax

Droot.right.val

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping min and max values.

Using root.right.val instead of root.val.

For the right subtree, the minimum allowed value is the current node's value, and max remains unchanged.

5fill in blank

hard

Fill all three blanks to complete the function signature and initial call for BST validation.

DSA Typescript

function isValidBST(root: TreeNode | null, [1]: number = -Infinity, [2]: number = [3]): boolean {
  if (root === null) return true;
  if (root.val <= min || root.val >= max) return false;
  return isValidBST(root.left, min, root.val) && isValidBST(root.right, root.val, max);
}

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

Amin

Bmax

CInfinity

Droot

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting default values causes errors.

Using wrong parameter names or default values.

The function uses min and max parameters with default values -Infinity and Infinity to check valid ranges.