Check if Two Trees are Symmetric in DSA C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean for two binary trees to be symmetric?

Two binary trees are symmetric if one is the mirror image of the other. This means the left subtree of one tree is the mirror of the right subtree of the other, and vice versa.

beginner

What is the base case when checking if two trees are symmetric?

If both trees are empty (null), they are symmetric. If only one is empty, they are not symmetric.

intermediate

How do you compare nodes when checking for symmetry?

Compare the values of the current nodes. Then recursively check if the left child of the first tree is symmetric with the right child of the second tree, and the right child of the first tree is symmetric with the left child of the second tree.

intermediate

Why is recursion a good approach to check tree symmetry?

Because symmetry involves comparing subtrees in a mirrored way, recursion naturally handles this by breaking the problem into smaller symmetric checks on child nodes.

intermediate

What is the time complexity of checking if two trees are symmetric?

The time complexity is O(n), where n is the number of nodes in the trees, because each node is visited once during the comparison.

What should you return if both input trees are null when checking symmetry?

A True

B False

C Null

D Error

If both trees are empty, they are symmetric by definition.

When comparing two nodes for symmetry, which children do you compare?

A Left child of first tree with left child of second tree

B Right child of first tree with right child of second tree

C Left child of first tree with right child of second tree

D None of the above

Symmetry means left subtree of one matches right subtree of the other.

If the root values of two trees differ, are the trees symmetric?

A Yes

B No

C Only if subtrees are symmetric

D Depends on tree height

Root values must be equal for trees to be symmetric.

What is the main technique used to check if two trees are symmetric?

A Recursion

B Iteration

C Sorting

D Hashing

Recursion is used to compare mirrored subtrees.

What is the worst-case time complexity to check if two trees with n nodes are symmetric?

A O(n^2)

B O(log n)

C O(1)

D O(n)

Each node is visited once, so time complexity is O(n).

Explain how to check if two binary trees are symmetric using recursion.

Think about mirror images and how left and right children relate.

Describe the time complexity and why it is that way when checking two trees for symmetry.

Consider how many nodes you check and how often.