Tree Traversal Preorder Root Left Right in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the root node's value first in preorder traversal.

DSA Go

func preorder(node *Node) {
    if node == nil {
        return
    }
    fmt.Println(node.[1])
}

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

ARight

BLeft

CValue

DParent

Attempts:

3 left

💡 Hint

Common Mistakes

Printing node.Left or node.Right instead of node.Value.

Trying to print node.Parent which may not exist.

In preorder traversal, we visit the root node first, so we print node.Value.

2fill in blank

medium

Complete the code to recursively traverse the left subtree in preorder.

DSA Go

func preorder(node *Node) {
    if node == nil {
        return
    }
    fmt.Println(node.Value)
    preorder(node.[1])
}

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

ARight

BLeft

CParent

DValue

Attempts:

3 left

💡 Hint

Common Mistakes

Calling preorder on node.Right instead of node.Left.

Calling preorder on node.Value which is not a node.

After visiting the root, preorder traversal visits the left subtree by calling preorder(node.Left).

3fill in blank

hard

Fix the error in the code to correctly traverse the right subtree in preorder.

DSA Go

func preorder(node *Node) {
    if node == nil {
        return
    }
    fmt.Println(node.Value)
    preorder(node.Left)
    preorder(node.[1])
}

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

ALeft

BValue

CParent

DRight

Attempts:

3 left

💡 Hint

Common Mistakes

Calling preorder on node.Value or node.Parent instead of node.Right.

Calling preorder on node.Left twice.

After visiting the left subtree, preorder traversal visits the right subtree by calling preorder(node.Right).

4fill in blank

hard

Fill both blanks to print the root node's value first and then recursively traverse the left subtree in preorder.

DSA Go

func preorder(node *Node) {
    if node == nil {
        return
    }
    fmt.Println(node.[1])
    preorder(node.[2])
}

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

AValue

BLeft

CRight

DParent

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping left and right child calls.

Printing node.Left instead of node.Value.

First print the root's value with node.Value, then recursively traverse the left subtree with preorder(node.Left).

5fill in blank

hard

Fill all three blanks to complete the preorder traversal visiting root, left, then right.

DSA Go

func preorder(node *Node) {
    if node == nil {
        return
    }
    fmt.Println(node.[1])
    preorder(node.[2])
    preorder(node.[3])
}

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

AValue

BLeft

CRight

DParent

Attempts:

3 left

💡 Hint

Common Mistakes

Calling preorder on node.Parent which is incorrect.

Mixing up left and right child calls.

Preorder traversal visits the root node's value, then recursively visits the left subtree, then the right subtree.

Practice

1. What is the order of nodes visited in a preorder tree traversal?

easy

A. Root, Left, Right

B. Left, Root, Right

C. Left, Right, Root

D. Right, Left, Root

Solution

1. Step 1: Understand preorder traversal definition

   Preorder traversal visits the root node first, then the left subtree, and finally the right subtree.

2. Step 2: Match the order with options

   Root, Left, Right matches the order Root, Left, Right exactly.

3. Final Answer:

   Root, Left, Right -> Option A

4. Quick Check:

   Preorder = Root, Left, Right [OK]

Hint: Remember preorder starts with root node first [OK]

Common Mistakes:

• Confusing preorder with inorder or postorder
• Swapping left and right subtree order
• Starting traversal from left child instead of root

2. Which of the following Go function signatures correctly represents a preorder traversal function for a binary tree node Node?

easy

A. func preorder(root *Node) { if root == nil { return } preorder(root.Left) preorder(root.Right) fmt.Println(root.Value) }

B. func preorder(root *Node) { if root == nil { return } fmt.Println(root.Value) preorder(root.Left) preorder(root.Right) }

C. func preorder(root *Node) { if root == nil { return } preorder(root.Right) fmt.Println(root.Value) preorder(root.Left) }

D. func preorder(root *Node) { if root == nil { return } preorder(root.Left) fmt.Println(root.Value) preorder(root.Right) }

Solution

1. Step 1: Recall preorder traversal order

   Preorder visits root first, then left subtree, then right subtree.

2. Step 2: Check function order

   func preorder(root *Node) { if root == nil { return } fmt.Println(root.Value) preorder(root.Left) preorder(root.Right) } prints root value first, then recursively visits left and right children, matching preorder.

3. Final Answer:

   func preorder(root *Node) { if root == nil { return } fmt.Println(root.Value) preorder(root.Left) preorder(root.Right) } -> Option B

4. Quick Check:

   Print root before children calls [OK]

Hint: Print root value before recursive calls [OK]

Common Mistakes:

• Printing after recursive calls (postorder)
• Swapping left and right recursive calls
• Missing nil check for root

3. Given the binary tree below, what is the preorder traversal output?

    10
   /  \
  5    15
 /    /  \
3    12  20

func preorder(root *Node) { if root == nil { return } fmt.Print(root.Value, " ") preorder(root.Left) preorder(root.Right) }

medium

A. [5, 3, 10, 15, 12, 20]

B. [3, 5, 10, 12, 15, 20]

C. [10, 15, 20, 12, 5, 3]

D. [10, 5, 3, 15, 12, 20]

Solution

1. Step 1: Start at root node 10

   Print 10, then traverse left subtree.

2. Step 2: Traverse left subtree (5, then 3)

   Print 5, then left child 3, which has no children.

3. Step 3: Traverse right subtree (15, 12, 20)

   Print 15, then left child 12, then right child 20.

4. Final Answer:

   [10, 5, 3, 15, 12, 20] -> Option D

5. Quick Check:

   Preorder = Root, Left, Right [OK]

Hint: Follow root, then left subtree, then right subtree order [OK]

Common Mistakes:

• Mixing preorder with inorder or postorder output
• Visiting right subtree before left
• Skipping leaf nodes

4. The following Go code attempts a preorder traversal but produces incorrect output. What is the error?

func preorder(root *Node) {
  if root == nil {
    return
  }
  preorder(root.Left)
  fmt.Print(root.Value, " ")
  preorder(root.Right)
}

medium

A. The function uses fmt.Print instead of fmt.Println

B. The function does not check for nil root

C. The root value is printed after left subtree traversal, not before

D. The right subtree is traversed before the left subtree

Solution

1. Step 1: Analyze print position in code

   The root value is printed after preorder(root.Left), so root is visited after left subtree.

2. Step 2: Compare with preorder definition

   Preorder requires visiting root first, then left, then right. This code visits left first, then root, then right (inorder).

3. Final Answer:

   The root value is printed after left subtree traversal, not before -> Option C

4. Quick Check:

   Print root before children for preorder [OK]

Hint: Print root value before recursive calls to fix order [OK]

Common Mistakes:

• Confusing preorder with inorder traversal
• Ignoring nil check (though present here)
• Thinking print function choice affects traversal order

5. You want to collect all node values of a binary tree in preorder traversal into a slice in Go. Which code snippet correctly does this?

hard

A. func preorder(root *Node, result *[]int) { if root == nil { return } *result = append(*result, root.Value) preorder(root.Left, result) preorder(root.Right, result) }

B. func preorder(root *Node, result []int) []int { if root == nil { return result } result = append(result, root.Value) preorder(root.Left, result) preorder(root.Right, result) return result }

C. func preorder(root *Node) []int { if root == nil { return nil } left := preorder(root.Left) right := preorder(root.Right) return append(left, append(right, root.Value)...) }

D. func preorder(root *Node, result *[]int) { if root == nil { return } preorder(root.Left, result) preorder(root.Right, result) *result = append(*result, root.Value) }

Solution

1. Step 1: Understand preorder collection logic

   Preorder means add root value first, then traverse left and right subtrees.

2. Step 2: Check each option's order and parameter usage

   func preorder(root *Node, result *[]int) { if root == nil { return } *result = append(*result, root.Value) preorder(root.Left, result) preorder(root.Right, result) } appends root value first, then recursively traverses left and right, using pointer to slice to collect values correctly.

3. Final Answer:

   func preorder(root *Node, result *[]int) { if root == nil { return } *result = append(*result, root.Value) preorder(root.Left, result) preorder(root.Right, result) } -> Option A

4. Quick Check:

   Append root first, use pointer to slice [OK]

Hint: Append root value before recursive calls, pass slice pointer [OK]

Common Mistakes:

• Appending after recursive calls (wrong order)
• Passing slice by value and expecting changes
• Appending right subtree before left subtree