Boundary Traversal of Binary Tree in DSA C++ - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Boundary Traversal for a Simple Tree

What is the output of the boundary traversal for the following binary tree?

Tree structure:
1
/ \
2 3
/ \ \
4 5 6
/ \
7 8

DSA C++

struct Node {
    int data;
    Node* left;
    Node* right;
};

// Boundary traversal prints nodes in this order:
// root, left boundary (excluding leaves), leaves, right boundary (excluding leaves, bottom-up)

// Given the tree above, what is the printed boundary traversal sequence?

A [1, 2, 4, 7, 8, 6, 3]

B [1, 2, 4, 7, 8, 6, 3, 5]

C [1, 2, 4, 5, 7, 8, 6, 3]

D [1, 2, 4, 7, 8, 5, 6, 3]

💡 Hint

Remember to exclude leaves from left and right boundaries and print leaves only once.

Boundary traversal includes root, left boundary excluding leaves, all leaves from left to right, and right boundary excluding leaves printed bottom-up. Node 5 is not part of left or right boundary but has leaves 7 and 8.

🧠 Conceptual

intermediate

Understanding Leaf Nodes in Boundary Traversal

In boundary traversal of a binary tree, which nodes are considered leaf nodes?

A Nodes on the left boundary only

B Nodes with only one child

C Nodes with no children (no left and no right child)

D Nodes on the right boundary only

💡 Hint

Think about what makes a node a leaf in any tree.

Leaf nodes are nodes that do not have any children, meaning both left and right pointers are null.

❓ Predict Output

advanced

Output of Boundary Traversal for a Complex Tree

What is the output of the boundary traversal for the following binary tree?

Tree structure:
10
/ \
20 30
/ / \
40 50 60
\ /
70 80
\
90

DSA C++

/* Boundary traversal order: root, left boundary (excluding leaves), leaves, right boundary (excluding leaves, bottom-up) */

A [10, 20, 40, 70, 50, 90, 80, 60]

B [10, 20, 40, 70, 50, 80, 90, 60, 30]

C [10, 20, 40, 70, 50, 90, 80, 30, 60]

D [10, 20, 40, 70, 50, 90, 80, 60, 30]

💡 Hint

Remember to print right boundary nodes bottom-up and include all leaves from left to right.

Left boundary excluding leaves: 20, 40 (70 is leaf). Leaves: 70, 50, 90. Right boundary excluding leaves: 60, 30 printed bottom-up as 60 then 30. Root is 10.

🔧 Debug

advanced

Identify the Error in Boundary Traversal Code

Given this snippet of C++ code for printing the left boundary of a binary tree, what error will it cause?

Code:
void printLeftBoundary(Node* root) {
if (!root) return;
if (root->left) {
cout << root->data << " ";
printLeftBoundary(root->left);
} else if (root->right) {
cout << root->data << " ";
printLeftBoundary(root->right);
}
// No else to handle leaf nodes
}

A Leaves on the left boundary will not be printed at all

B Leaves on the left boundary will be printed twice

C Code will cause a segmentation fault

D Code will print right boundary nodes instead of left

💡 Hint

Check what happens when the node is a leaf (no left or right child).

The code does not print leaf nodes because it only prints when left or right child exists. Leaves are skipped here.

🚀 Application

expert

Number of Nodes in Boundary Traversal

Consider a perfect binary tree of height 3 (levels 0 to 3). How many nodes will be printed in its boundary traversal?

A 10

B 14

C 12

D 15

💡 Hint

Count root, left boundary excluding leaves, leaves, and right boundary excluding leaves carefully.

A perfect binary tree of height 3 has 15 nodes. Leaves are all nodes at level 3 (8 nodes). Left boundary excluding leaves has 2 nodes, right boundary excluding leaves has 2 nodes, plus root (1). Total = 1 + 2 + 8 + 2 = 13 but root is counted once, so total 14 nodes.