Validate if Tree is BST in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Go

if [1] == nil {
    return true
}

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Anode

Broot

Ctree

DrootNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'root' instead of 'node' causes confusion in recursion.

Checking for 'tree' or 'rootNode' which are not defined in this scope.

We check if the current node (named 'node') is nil to stop recursion.

2fill in blank

medium

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

DSA Go

if node.Val <= [1] || node.Val >= [2] {
    return false
}

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Amin

Bmax

Cleft

Dright

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'left' or 'right' instead of min and max confuses the range check.

Using >= for min or <= for max reverses the logic.

The node's value must be greater than min and less than max to be valid in BST.

3fill in blank

hard

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

DSA Go

return isValidBSTHelper(node.Left, [1], node.Val) && isValidBSTHelper(node.Right, node.Val, [2])

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Amin

Bnode.Val

Cmax

Dnil

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping min and max in recursive calls.

Passing nil instead of boundaries causes runtime errors.

For the left subtree, max becomes node.Val; for the right subtree, min becomes node.Val.

4fill in blank

hard

Fill both blanks to initialize the min and max values for the first call to isValidBST.

DSA Go

func isValidBST(root *TreeNode) bool {
    return isValidBSTHelper(root, [1], [2])
}

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Amath.MinInt64

Bmath.MaxInt64

C0

Dnil

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 for boundaries restricts valid values incorrectly.

Using nil causes type errors in Go.

We start with the smallest and largest possible integer values as boundaries.

5fill in blank

hard

Fill all three blanks to complete the helper function signature and recursive calls correctly.

DSA Go

func isValidBSTHelper(node *TreeNode, [1] int64, [2] int64) bool {
    if node == nil {
        return true
    }
    if node.Val <= [1] || node.Val >= [2] {
        return false
    }
    return isValidBSTHelper(node.Left, [1], node.Val) && isValidBSTHelper(node.Right, node.Val, [2])
}

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Amin

Bmax

Cval

DnodeVal

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent parameter names causes confusion.

Passing wrong variables in recursive calls.

The helper takes min and max as int64 boundaries; node.Val is checked against min and max.