Lowest Common Ancestor in Binary Tree in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the current node is null.

DSA C++

if (root == [1]) return nullptr;

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

A0

BNULL

Cnullptr

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or NULL instead of nullptr

Checking for false instead of nullptr

We check if the root pointer is nullptr to know if we reached the end of a branch.

2fill in blank

medium

Complete the code to check if the current node matches either of the target nodes.

DSA C++

if (root->val == [1] || root->val == q->val || root->val == p->val) return root;

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

Anullptr

Bp->val

Croot->val

Dq->val

Attempts:

3 left

💡 Hint

Common Mistakes

Using root->val instead of p->val

Using nullptr instead of a value

We check if the current node's value matches p->val or q->val. Here, the blank is for p->val.

3fill in blank

hard

Fix the error in the recursive calls to search left and right subtrees.

DSA C++

TreeNode* left = [1](root->left, p, q);
TreeNode* right = lowestCommonAncestor(root->right, p, q);

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

AlowestCommonAncestor

BfindAncestor

ClowestCommon

DcommonAncestor

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined function names

Typos in function name

The function calls itself recursively, so the function name must be lowestCommonAncestor.

4fill in blank

hard

Fill both blanks to return the correct ancestor based on left and right subtree results.

DSA C++

if (left != [1] && right != [2]) return root;

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

Anullptr

BNULL

C0

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL or 0 instead of nullptr

Using false which is incorrect

We check if both left and right are not nullptr, meaning both subtrees contain one of the nodes, so current root is the ancestor.

5fill in blank

hard

Fill all three blanks to return the non-null subtree result or nullptr if none found.

DSA C++

return left != [1] ? left : (right != [2] ? right : [3]);

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

Anullptr

BNULL

Cfalse

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using NULL or 0 instead of nullptr

Using false which is incorrect

We return left if it is not nullptr, else right if it is not nullptr, else nullptr.