Validate if Tree is BST in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA C++

if (root == [1]) return true;

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A0

Bnullptr

CNULL

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or NULL instead of nullptr

Returning false instead of true here

We check if the node pointer is nullptr to know if we reached a leaf's child.

2fill in blank

medium

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

DSA C++

if (root->val <= [1] || root->val >= maxVal) return false;

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Aroot->val

BmaxVal

CminVal

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using maxVal instead of minVal here

Comparing with root->val itself

We check if the node's value is less than or equal to minVal or greater than or equal to maxVal.

3fill in blank

hard

Fix the error in the recursive call to validate the left subtree.

DSA C++

return isValidBST(root->left, [1], root->val) && isValidBST(root->right, root->val, maxVal);

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

AminVal

Bnullptr

Croot->val

DmaxVal

Attempts:

3 left

💡 Hint

Common Mistakes

Using maxVal instead of minVal for left subtree

Passing nullptr instead of a value

The left subtree must have values less than the current node's value, so pass minVal as lower bound and update max to root->val.

4fill in blank

hard

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

DSA C++

bool isValidBST(TreeNode* root, [1] minVal = [2], long maxVal = LONG_MAX) {

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Along

Bint

Cnullptr

DLONG_MIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using int instead of long

Using nullptr as default for minVal

The function uses long type for minVal and maxVal to handle edge cases. The initial minVal is set to LONG_MIN.

5fill in blank

hard

Fill all three blanks to complete the recursive BST validation logic.

DSA C++

if (root == nullptr) return true;
if (root->val <= [1] || root->val >= [2]) return false;
return isValidBST(root->left, [1], root->val) && isValidBST(root->right, root->val, [2]);

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

AminVal

BmaxVal

Croot->val

Dnullptr

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up minVal and maxVal

Using root->val incorrectly in comparisons

The node's value must be greater than minVal and less than maxVal. The recursive calls update these bounds accordingly.