Top View of Binary Tree in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the structure for a binary tree node.

DSA C

struct Node {
    int data;
    struct Node* [1];
    struct Node* right;
};

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

Aleft

Bchild

Cprev

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'child' or 'next' instead of 'left' for the left child pointer.

The left child pointer in a binary tree node is usually named 'left'.

2fill in blank

easy

Fill the blanks to complete the main function that initializes and calls the top view utility.

DSA C

int main() {
    struct Node* root = newNode(1);
    root->left = newNode(2);
    root->right = newNode(3);
    int minHd = 0, maxHd = 0;
    int visited[100] = {0};
    topViewUtil(root, [1], &minHd, &maxHd, visited);
    return [2];
}

struct Node* newNode(int data) {
    struct Node* node = (struct Node*)malloc(sizeof(struct Node));
    node->data = data;
    node->left = NULL;
    node->right = NULL;
    return node;
}

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

A1

B0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 instead of 0 for horizontal distance or return value.

The initial horizontal distance for the root is 0. The main function should return 0 upon successful execution.

3fill in blank

medium

Complete the code to create a new node with given data.

DSA C

struct Node* newNode(int data) {
    struct Node* node = (struct Node*)malloc(sizeof(struct Node));
    node->data = data;
    node->left = NULL;
    node->[1] = NULL;
    return node;
}

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

Achild

Bparent

Cnext

Dright

Attempts:

3 left

💡 Hint

Common Mistakes

Initializing wrong pointer like 'parent' or 'next' instead of 'right'.

The right child pointer must be initialized to NULL when creating a new node.

4fill in blank

medium

Complete the code to print the level order traversal of the binary tree using a queue.

DSA C

void topView(struct Node* root) {
    if (root == NULL) return;
    struct Queue* q = createQueue();
    enqueue(q, root);
    while (!isEmpty(q)) {
        struct Node* temp = dequeue(q);
        printf("%d ", temp->data);
        if (temp->left) enqueue(q, temp->[1]);
        if (temp->right) enqueue(q, temp->right);
    }
}

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

Aparent

Bleft

Cnext

Dchild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'temp->parent' or 'temp->next' instead of 'temp->left'.

In level order traversal using queue, enqueue the left child first, then the right child.

5fill in blank

hard

Fill both blanks to complete the function that stores the first node at each horizontal distance for top view.

DSA C

void topViewUtil(struct Node* root, int hd, int* minHd, int* maxHd, int* visited) {
    if (root == NULL) return;
    if(hd < *minHd) *minHd = hd;
    if(hd > *maxHd) *maxHd = hd;
    topViewUtil(root->[1], hd - 1, minHd, maxHd, visited);
    if (visited[hd + 50] == 0) {
        printf("%d ", root->data);
        visited[hd + 50] = 1;
    }
    topViewUtil(root->[2], hd + 1, minHd, maxHd, visited);
}

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

Aleft

Bright

Cparent

Dchild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'parent' or 'child' instead of 'left' or 'right'.

Traverse left child with 'root->left' (decrement hd) and right child with 'root->right' (increment hd).

Practice

1. What does the top view of a binary tree represent?

easy

A. Nodes visible when the tree is viewed from the top

B. Nodes visible when the tree is viewed from the left side

C. Nodes visible when the tree is viewed from the right side

D. All leaf nodes of the tree

Solution

1. Step 1: Understand the meaning of top view

   The top view of a binary tree shows nodes visible when looking down vertically from above the tree.

2. Step 2: Compare with other views

   Left or right views show nodes from side angles, and leaf nodes are only the bottom nodes, not the top view.

3. Final Answer:

   Nodes visible when the tree is viewed from the top -> Option A

4. Quick Check:

   Top view = nodes seen from above [OK]

Hint: Top view shows nodes visible from above the tree [OK]

Common Mistakes:

• Confusing top view with left or right view
• Thinking top view includes all leaf nodes
• Assuming top view shows all nodes

2. Which data structure is commonly used to find the top view of a binary tree in C?

easy

A. Stack

B. Queue

C. Hash Map

D. Linked List

Solution

1. Step 1: Identify traversal method for top view

   Top view is found using level order traversal, which uses a queue to process nodes level by level.

2. Step 2: Understand role of queue

   Queue helps visit nodes in order from top to bottom and left to right, needed for correct top view.

3. Final Answer:

   Queue -> Option B

4. Quick Check:

   Level order traversal uses queue [OK]

Hint: Use queue for level order traversal in top view [OK]

Common Mistakes:

• Using stack which is for depth-first traversal
• Confusing hash map as traversal structure
• Using linked list instead of queue

3. What is the output top view of the binary tree below?

        1
       / \
      2   3
       \   \
        4   5
         \   \
          6   7

medium

A. [1, 2, 3, 4, 5]

B. [2, 1, 4, 6, 7]

C. [2, 1, 3, 4, 7]

D. [2, 1, 3, 5, 7]

Solution

1. Step 1: Assign horizontal distances

   Assign horizontal distance (HD) from root: root(1) = 0, left child decreases HD by 1, right child increases HD by 1. So, 2 = -1, 3 = 1, 4 = 0, 5 = 2, 6 = 1, 7 = 3.

2. Step 2: Select topmost nodes at each HD

   At HD -1: 2; HD 0: 1 (4 is lower); HD 1: 3 (6 is lower); HD 2: 5; HD 3: 7.

3. Final Answer:

   [2, 1, 3, 5, 7] -> Option D

4. Quick Check:

   Top view nodes by HD = [2,1,3,5,7] [OK]

Hint: Use horizontal distance and pick top nodes [OK]

Common Mistakes:

• Choosing lower nodes instead of top nodes
• Ignoring horizontal distance concept
• Mixing order of nodes in output

4. Consider this C code snippet to print top view of a binary tree:

void topView(Node* root) {
    if (!root) return;
    map topNode;
    queue> q;
    q.push({root, 0});
    while (!q.empty()) {
        auto p = q.front(); q.pop();
        Node* node = p.first;
        int hd = p.second;
        if (topNode.find(hd) == topNode.end())
            topNode[hd] = node->data;
        if (node->left) q.push({node->left, hd - 1});
        if (node->right) q.push({node->right, hd + 1});
    }
    for (auto it : topNode)
        cout << it.second << " ";
}

What is the error in this code?

medium

A. Incorrect horizontal distance calculation

B. Not checking if root is NULL

C. Using C++ STL map and queue in C code

D. Missing return statement in void function

Solution

1. Step 1: Identify language mismatch

   The code uses C++ STL containers like map and queue, but the function is declared in C style which does not support these STL features.

2. Step 2: Check other code parts

   Root NULL check is present, horizontal distance is correctly updated, and void functions do not require return statements.

3. Final Answer:

   Using C++ STL map and queue in C code -> Option C

4. Quick Check:

   C code cannot use C++ STL containers [OK]

Hint: C code can't use C++ STL containers like map or queue [OK]

Common Mistakes:

• Ignoring language differences between C and C++
• Thinking void functions need return
• Assuming horizontal distance logic is wrong

5. You have a binary tree where multiple nodes share the same horizontal distance and level. How should you modify the top view algorithm to always show the leftmost node at that horizontal distance?

hard

A. Store the first node encountered at each horizontal distance during level order traversal

B. Store the last node encountered at each horizontal distance during level order traversal

C. Store nodes with maximum depth at each horizontal distance

D. Store nodes with minimum depth at each horizontal distance but prefer right child first

Solution

1. Step 1: Understand node selection in top view

   Top view shows the first node encountered at each horizontal distance during level order traversal, which naturally picks the leftmost node at that distance.

2. Step 2: Avoid overwriting nodes

   By storing only the first node at each horizontal distance and ignoring later nodes, the leftmost node is preserved.

3. Final Answer:

   Store the first node encountered at each horizontal distance during level order traversal -> Option A

4. Quick Check:

   First node at HD = leftmost node [OK]

Hint: Keep first node per horizontal distance in level order [OK]

Common Mistakes:

• Overwriting with last node instead of first
• Choosing nodes by max depth instead of min
• Preferring right child first breaks leftmost rule