Count Total Nodes in Binary Tree in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return 0 when the node is empty (nil).

DSA Go

func countNodes(root *TreeNode) int {
    if root == [1] {
        return 0
    }
    return 1 + countNodes(root.Left) + countNodes(root.Right)
}

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

Anull

Bnil

C0

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'null' instead of 'nil' causes a compile error.

Returning 0 without checking for nil causes runtime errors.

In Go, the empty pointer is represented by nil. So we check if root == nil to handle the base case.

2fill in blank

medium

Complete the code to count nodes by adding 1 for the current node plus counts of left and right subtrees.

DSA Go

func countNodes(root *TreeNode) int {
    if root == nil {
        return 0
    }
    return [1] + countNodes(root.Left) + countNodes(root.Right)
}

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

A1

B0

Croot.Val

DcountNodes(root)

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 0 instead of 1 results in always zero count.

Using root.Val adds node value, not count.

We add 1 for the current node, then recursively count left and right subtrees.

3fill in blank

hard

Fix the error in the recursive call to count left subtree nodes.

DSA Go

func countNodes(root *TreeNode) int {
    if root == nil {
        return 0
    }
    return 1 + countNodes([1]) + countNodes(root.Right)
}

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Anil

Broot.Right

Croot

Droot.Left

Attempts:

3 left

💡 Hint

Common Mistakes

Using root.Right twice counts right subtree twice.

Using root or nil causes infinite recursion or errors.

To count left subtree nodes, we must call countNodes on root.Left.

4fill in blank

hard

Fill both blanks to complete the function that counts nodes in a binary tree.

DSA Go

func countNodes(root *TreeNode) int {
    if root == [1] {
        return [2]
    }
    return 1 + countNodes(root.Left) + countNodes(root.Right)
}

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

Anil

B0

C1

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 1 when root is nil inflates count.

Checking for 'empty' instead of nil causes errors.

When root is nil, return 0 because there are no nodes to count.

5fill in blank

hard

Fill all three blanks to complete the recursive count function with base case and recursive calls.

DSA Go

func countNodes(root *TreeNode) int {
    if root == [1] {
        return [2]
    }
    return [3] + countNodes(root.Left) + countNodes(root.Right)
}

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

Anil

B0

C1

Droot

Attempts:

3 left

💡 Hint

Common Mistakes

Returning root instead of 0 in base case.

Adding 0 instead of 1 for current node.

Base case returns 0 if node is nil; otherwise add 1 for current node plus counts of left and right.