89 Lowest common ancestor Medium Recursive Descent

Find the deepest node in a binary tree that is an ancestor of both given nodes.

O(n) time · O(h) space
90 Diameter of binary tree Easy Recursive Max

Find the longest path between any two nodes in a binary tree, measured in edges.

O(n) time · O(h) space
91 Serialize and deserialize BST Medium Preorder

Convert a binary tree to a string so it can be saved, then rebuild the tree from that string.

O(n) time · O(n) space
92 Path sum Easy Recursive Descent

Check if any path from the root to a leaf adds up to a given target number.

O(n) time · O(h) space
93 Binary tree right side view Medium Queue by Level

Look at a binary tree from the right side and list the nodes you can see at each level.

O(n) time · O(n) space
94 Symmetric tree Easy Recursive Max

Check whether the left and right halves of a binary tree are mirror images of each other.

O(n) time · O(h) space