Mirror a Binary Tree in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap the left and right child nodes of the root.

DSA C++

void mirror(Node* root) {
    if (root == nullptr) return;
    Node* temp = root->left;
    root->left = root->[1];
    root->right = temp;
}

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Aparent

Bleft

Cright

Dchild

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning root->left to root->left again instead of root->right.

Swapping with a wrong pointer like parent or child.

We swap the left child with the right child, so root->left should be assigned root->right.

2fill in blank

medium

Complete the code to recursively mirror the left subtree.

DSA C++

void mirror(Node* root) {
    if (root == nullptr) return;
    mirror(root->[1]);
    mirror(root->right);
    Node* temp = root->left;
    root->left = root->right;
    root->right = temp;
}

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Aleft

Bright

Cparent

Dchild

Attempts:

3 left

💡 Hint

Common Mistakes

Calling mirror on root->right twice.

Calling mirror on an invalid pointer like parent.

We need to recursively mirror the left subtree, so we call mirror on root->left.

3fill in blank

hard

Fix the error in the base case check to avoid null pointer dereference.

DSA C++

void mirror(Node* root) {
    if (root == [1]) return;
    mirror(root->left);
    mirror(root->right);
    Node* temp = root->left;
    root->left = root->right;
    root->right = temp;
}

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ANULL

Bnullptr

C0

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL which is legacy and less type-safe.

Using 0 or false which are not pointers.

In modern C++, nullptr is the correct way to check for a null pointer.

4fill in blank

hard

Fill both blanks to complete the recursive mirror function correctly.

DSA C++

void mirror(Node* root) {
    if (root == [1]) return;
    mirror(root->[2]);
    mirror(root->right);
    Node* temp = root->left;
    root->left = root->right;
    root->right = temp;
}

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Anullptr

Bleft

Cright

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong null check values.

Recursing on the wrong child pointer.

The base case checks if root is nullptr, and then we recursively call mirror on root->left before swapping.

5fill in blank

hard

Fill all three blanks to implement the mirror function with both recursive calls and swapping.

DSA C++

void mirror(Node* root) {
    if (root == [1]) return;
    mirror(root->[2]);
    mirror(root->[3]);
    Node* temp = root->left;
    root->left = root->right;
    root->right = temp;
}

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

Anullptr

Bleft

Cright

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Missing one of the recursive calls.

Incorrect null check.

Check for nullptr, then recursively mirror left and right subtrees before swapping children.