Check if Two Trees are Symmetric in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if two nodes are both null.

DSA C++

if (root1 == nullptr && root2 [1] nullptr) return true;

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

A==

B&&

C!=

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using && causes a syntax error (root2 && nullptr).

Using != checks if root2 is not null, which is incorrect.

Using || changes the logic to OR, which is wrong.

We check if both root1 and root2 are null by using == to compare root2 with nullptr.

2fill in blank

medium

Complete the code to check if one node is null and the other is not.

DSA C++

if (root1 == nullptr || root2 [1] nullptr) return false;

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

A&&

B==

C!=

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using != fails to detect root1 non-null and root2 null.

Using && requires both null, already handled.

Using || is misplaced; it's already between conditions.

Since the both-null case is handled earlier, we check if root1 == nullptr || root2 == nullptr to catch exactly one null.

3fill in blank

hard

Fix the error in comparing node values for symmetry.

DSA C++

if (root1->val [1] root2->val) return false;

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

A==

B>

C!=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using == returns false when values are equal, which is wrong.

Using < or > is not correct for equality check.

We return false if the values are not equal, so we use !=.

4fill in blank

hard

Fill both blanks to recursively check left and right subtrees for symmetry.

DSA C++

return isSymmetricHelper(root1->[1], root2->[2]) && isSymmetricHelper(root1->[2], root2->[1]);

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

Aleft

Bright

Cval

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping left and right incorrectly.

Using 'val' or 'parent' instead of child pointers.

We compare root1's left with root2's right and root1's right with root2's left for symmetry.

5fill in blank

hard

Fill all three blanks to complete the main function calling the helper.

DSA C++

bool isSymmetric(TreeNode* root) {
    if (root == nullptr) return true;
    return isSymmetricHelper(root->[1], root->[2]);
}

bool isSymmetricHelper(TreeNode* root1, TreeNode* root2) {
    if (root1 == nullptr && root2 == nullptr) return true;
    if (root1 == nullptr || root2 [3] nullptr) return false;
    if (root1->val != root2->val) return false;
    return isSymmetricHelper(root1->left, root2->right) && isSymmetricHelper(root1->right, root2->left);
}

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

Aleft

Bright

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Passing root itself instead of children.

Using != instead of == in null check.

The main function calls helper with root's left and right children. The helper checks if one node is null and the other is not using ==.