Diameter of Binary Tree in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the TreeNode struct with integer value and pointers to left and right children.

DSA Go

type TreeNode struct {
    Val   int
    Left  *[1]
    Right *TreeNode
}

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

ABinaryNode

BTree

CTreeNode

DNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different struct name for the child pointers.

Forgetting the pointer symbol '*' before the struct name.

The left child pointer must be of type *TreeNode to correctly reference the same struct type.

2fill in blank

medium

Complete the code to calculate the maximum of two integers a and b.

DSA Go

func max(a, b int) int {
    if a [1] b {
        return a
    }
    return b
}

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

A<

B>

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causing minimum to be returned.

Using '==' which only checks equality.

To return the maximum, check if a is greater than b.

3fill in blank

hard

Fix the error in the recursive function to compute the height of a binary tree node.

DSA Go

func height(root *TreeNode) int {
    if root == nil {
        return 0
    }
    leftHeight := height(root.[1])
    rightHeight := height(root.Right)
    if leftHeight > rightHeight {
        return leftHeight + 1
    }
    return rightHeight + 1
}

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

ARight

Bleft

Cright

DLeft

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'left' which causes compilation error.

Confusing 'Right' and 'left' fields.

The field name is 'Left' with uppercase L as per Go struct field naming conventions.

4fill in blank

hard

Fill both blanks to update the diameter and return the height of the current node.

DSA Go

func diameterHelper(root *TreeNode, diameter *int) int {
    if root == nil {
        return 0
    }
    leftHeight := diameterHelper(root.Left, diameter)
    rightHeight := diameterHelper(root.Right, diameter)
    *diameter = max(*diameter, leftHeight [1] rightHeight)
    return max(leftHeight, rightHeight) [2] 1
}

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

A+

B*

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication or subtraction instead of addition.

Returning sum instead of max for height.

The diameter is updated by sum of left and right heights; height is max of left/right plus 1.

5fill in blank

hard

Fill all three blanks to implement the diameter of binary tree function using helper.

DSA Go

func diameterOfBinaryTree(root *TreeNode) int {
    diameter := 0
    var [1] func(*TreeNode) int
    [1] = func(node *TreeNode) int {
        if node == nil {
            return 0
        }
        left := [2](node.Left)
        right := [2](node.Right)
        if left + right > diameter {
            diameter = left + right
        }
        if left > right {
            return left + 1
        }
        return right + 1
    }
    [1](root)
    return diameter
}

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

Aheight

BdiameterHelper

CheightHelper

DcalcHeight

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for function definition and calls causing errors.

Not updating diameter correctly inside helper.

The anonymous function is named 'height' and recursively called to compute heights and update diameter.

Practice

1. What does the diameter of a binary tree represent?

easy

A. The length of the longest path between any two nodes in the tree

B. The number of nodes in the tree

C. The height of the tree

D. The number of leaf nodes in the tree

Solution

1. Step 1: Understand the diameter definition

   The diameter is the longest path between any two nodes, which may or may not pass through the root.

2. Step 2: Differentiate from other tree properties

   Height is the longest path from root to leaf, number of nodes counts all nodes, leaves count only leaf nodes.

3. Final Answer:

   The length of the longest path between any two nodes in the tree -> Option A

4. Quick Check:

   Diameter = longest path between nodes [OK]

Hint: Diameter is longest path, not height or node count [OK]

Common Mistakes:

• Confusing diameter with height
• Thinking diameter counts nodes instead of edges
• Assuming diameter must pass through root

2. Which Go function signature correctly represents a helper function to compute the height of a binary tree node for diameter calculation?

easy

A. func height(node int) int

B. func height(node *TreeNode) int

C. func height(node *TreeNode) bool

D. func height(node TreeNode) string

Solution

1. Step 1: Identify correct parameter type

   The function should accept a pointer to TreeNode to handle nil nodes and avoid copying.

2. Step 2: Identify correct return type

   Height is an integer value representing depth, so return type must be int.

3. Final Answer:

   func height(node *TreeNode) int -> Option B

4. Quick Check:

   Pointer input and int output for height [OK]

Hint: Height function uses pointer receiver and returns int [OK]

Common Mistakes:

• Using value receiver instead of pointer
• Returning wrong type like string or bool
• Passing int instead of TreeNode pointer

3. Given the following Go code snippet, what is the diameter of the binary tree?

type TreeNode struct {
    Val int
    Left *TreeNode
    Right *TreeNode
}

root := &TreeNode{Val: 1}
root.Left = &TreeNode{Val: 2}
root.Right = &TreeNode{Val: 3}
root.Left.Left = &TreeNode{Val: 4}
root.Left.Right = &TreeNode{Val: 5}

// Diameter function uses height helper internally
func diameterOfBinaryTree(root *TreeNode) int {
    maxDiameter := 0
    var height func(node *TreeNode) int
    height = func(node *TreeNode) int {
        if node == nil {
            return 0
        }
        leftHeight := height(node.Left)
        rightHeight := height(node.Right)
        if leftHeight+rightHeight > maxDiameter {
            maxDiameter = leftHeight + rightHeight
        }
        if leftHeight > rightHeight {
            return leftHeight + 1
        }
        return rightHeight + 1
    }
    height(root)
    return maxDiameter
}

fmt.Println(diameterOfBinaryTree(root))

medium

A. 4

B. 2

C. 3

D. 5

Solution

1. Step 1: Calculate heights of subtrees

   Left subtree of root has height 2 (nodes 2->4 or 2->5), right subtree height is 1 (node 3).

2. Step 2: Calculate diameter as sum of left and right heights

   Diameter = leftHeight + rightHeight = 2 + 1 = 3 edges, but diameter counts edges, so longest path is 3 edges which means 4 nodes.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   Longest path length = 3 edges [OK]

Hint: Diameter = sum of left and right subtree heights at max node [OK]

Common Mistakes:

• Counting nodes instead of edges for diameter
• Ignoring one subtree height
• Confusing height with diameter

4. Identify the bug in this Go code snippet for computing the diameter of a binary tree:

func diameterOfBinaryTree(root *TreeNode) int {
    maxDiameter := 0
    var height func(node *TreeNode) int
    height = func(node *TreeNode) int {
        if node == nil {
            return 0
        }
        leftHeight := height(node.Left)
        rightHeight := height(node.Right)
        maxDiameter = leftHeight + rightHeight
        if leftHeight > rightHeight {
            return leftHeight + 1
        }
        return rightHeight + 1
    }
    height(root)
    return maxDiameter
}

medium

A. Function does not call height recursively

B. height function returns wrong type

C. Missing base case for nil node

D. maxDiameter is overwritten without checking max value

Solution

1. Step 1: Analyze maxDiameter update

   maxDiameter is assigned leftHeight + rightHeight every time, overwriting previous max without comparison.

2. Step 2: Correct maxDiameter update

   Should update maxDiameter only if leftHeight + rightHeight is greater than current maxDiameter.

3. Final Answer:

   maxDiameter is overwritten without checking max value -> Option D

4. Quick Check:

   Use max check before assignment [OK]

Hint: Update maxDiameter only if new value is greater [OK]

Common Mistakes:

• Overwriting maxDiameter without max check
• Forgetting base case for nil node
• Not calling height recursively

5. You want to find the diameter of a binary tree but also return the path nodes forming that diameter. Which approach correctly extends the diameter calculation in Go?

hard

A. Modify height function to return both height and path, update max path when diameter increases

B. Calculate diameter first, then do a separate BFS to find path

C. Store all paths in a global slice and pick the longest after traversal

D. Use only height function and return diameter length without path

Solution

1. Step 1: Extend height function to track paths

   Modify the recursive height function to return both height and the path nodes from current node to leaf.

2. Step 2: Update max diameter and store path

   When leftHeight + rightHeight exceeds maxDiameter, update maxDiameter and store concatenated path from left and right subtrees through current node.

3. Step 3: Return stored path after traversal

   After full traversal, return the stored path representing the diameter.

4. Final Answer:

   Modify height function to return both height and path, update max path when diameter increases -> Option A

5. Quick Check:

   Track height and path together for diameter path [OK]

Hint: Return height and path from helper to track diameter path [OK]

Common Mistakes:

• Trying to find path after diameter without tracking
• Storing all paths wastes memory
• Ignoring path tracking in recursion