Check if Two Trees are Symmetric in DSA Javascript - 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 tree, 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 allows checking smaller parts of the trees step-by-step until reaching the base case.

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 Error

B False

C Null

D True

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 right child of second tree

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

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

D None of the above

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

If one tree node is null and the other is not, are the trees symmetric?

A Only if values match

B Yes

C No

D Depends on tree height

One null and one non-null node means trees differ, so not symmetric.

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

A Recursion

B Sorting

C Iteration

D Hashing

Recursion helps compare subtrees in mirrored order easily.

What is the time complexity of checking symmetry for two trees with n nodes?

A O(1)

B O(n)

C O(log n)

D O(n^2)

Each node is visited once, so time complexity is linear in number of nodes.

Explain step-by-step how to check if two binary trees are symmetric.

Think about mirror image and recursion base cases.

Describe why recursion is suitable for checking tree symmetry and what the base cases are.

Consider how trees are structured and how recursion explores them.