Check if Binary Tree is Balanced in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the height of the tree.

DSA C++

int height(TreeNode* root) {
    if (root == nullptr) return [1];
    return 1 + std::max(height(root->left), height(root->right));
}

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

A-1

B1

C0

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 1 instead of 0 for an empty tree.

Returning NULL which is not an integer.

The height of an empty tree is 0.

2fill in blank

medium

Complete the code to check if the height difference between left and right subtrees is more than 1.

DSA C++

bool isBalanced(TreeNode* root) {
    if (root == nullptr) return true;
    int lh = height(root->left);
    int rh = height(root->right);
    if (std::abs(lh - rh) > [1]) return false;
    return isBalanced(root->left) && isBalanced(root->right);
}

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

A0

B-1

C2

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 which means no difference allowed.

Using 2 which is too large.

A binary tree is balanced if the height difference between left and right subtree is at most 1.

3fill in blank

hard

Fix the error in the height function to avoid redundant calls.

DSA C++

int height(TreeNode* root) {
    if (root == nullptr) return 0;
    int lh = height(root->left);
    int rh = height(root->right);
    if (lh == -1 || rh == -1 || std::abs(lh - rh) > 1) return [1];
    return 1 + std::max(lh, rh);
}

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

A0

B-1

C1

DINT_MIN

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 0 which is a valid height.

Returning INT_MIN which is not standard here.

Return -1 to indicate the tree is not balanced at this node.

4fill in blank

hard

Fill both blanks to complete the optimized balanced check function.

DSA C++

int checkHeight(TreeNode* root) {
    if (root == nullptr) return [1];
    int lh = checkHeight(root->left);
    if (lh == [2]) return -1;
    int rh = checkHeight(root->right);
    if (rh == -1) return -1;
    if (std::abs(lh - rh) > 1) return -1;
    return 1 + std::max(lh, rh);
}

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

A0

B-1

C1

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Returning NULL which is not an int.

Not checking for -1 to propagate imbalance.

Return 0 for empty tree height and -1 to indicate imbalance.

5fill in blank

hard

Fill all three blanks to complete the final balanced tree check function.

DSA C++

bool isBalanced(TreeNode* root) {
    return checkHeight(root) != [1];
}

int checkHeight(TreeNode* root) {
    if (root == nullptr) return [2];
    int lh = checkHeight(root->left);
    if (lh == [3]) return -1;
    int rh = checkHeight(root->right);
    if (rh == -1) return -1;
    if (std::abs(lh - rh) > 1) return -1;
    return 1 + std::max(lh, rh);
}

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

A-1

B0

C1

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL which is not an int.

Not comparing checkHeight result to -1.

The function returns false if checkHeight returns -1 indicating imbalance.

Empty tree height is 0.

-1 signals imbalance.