Lowest Common Ancestor (LCA) Finding — Tree Traversal Patterns (DFS & BFS)
The Lowest Common Ancestor (LCA) Finding pattern applies when you need the Lowest Common Ancestor (LCA) Finding technique within the Tree Traversal Patterns (DFS & BFS) pattern. Its time complexity is O(n) and space complexity O(h). It is used in 2 problems on Thita, including Lowest Common Ancestor of a Binary Search Tree and Lowest Common Ancestor of a Binary Tree. Common variations are Recursive Preorder Traversal and Recursive Inorder Traversal.
Find lowest common ancestor in binary trees and BSTs using recursive and iterative approaches.
Lowest Common Ancestor (LCA) Finding is one of the 6 subpatterns of the Tree Traversal Patterns (DFS & BFS) pattern, which covers preorder, inorder, level order traversal, LCA, and serialization. The whole pattern is about 3 hours of study. This subpattern is a core technique: expect it to come up directly in interviews.
What Lowest Common Ancestor (LCA) Finding covers
Master tree traversal including preorder, inorder, postorder DFS, level order BFS, lowest common ancestor, and tree serialization techniques. Problems in this subpattern are usually searched for as lowest common ancestor, LCA, common ancestor, BST LCA, leetcode 236, leetcode 235.
How to practise Lowest Common Ancestor (LCA) Finding on Thita.ai
Read the theory for Lowest Common Ancestor (LCA) Finding, then work the problems attached to it in the browser editor. Your solution runs against the problem's test cases, and the AI coach offers a hint about the technique you are missing rather than a finished solution. Progress is tracked per subpattern, so the Tree Traversal Patterns (DFS & BFS) tracker shows this one as covered once you have solved its problems.
Other subpatterns in Tree Traversal Patterns (DFS & BFS)
- Recursive Preorder Traversal — Master preorder traversal for tree construction, inversion, and path problems. Visit root before children.
- Recursive Inorder Traversal — Master inorder traversal for BST validation and kth element problems. Produces sorted order in BST.
- Level Order Traversal — Master level order traversal using BFS. Solve zigzag, right side view, and level sum problems.
- Recursive Postorder Traversal — Master postorder traversal for tree height, diameter, and path sum problems. Process children before root.
- Serialization and Deserialization — Learn to serialize and deserialize binary trees. Convert trees to strings and reconstruct them.
Related DSA patterns
- Stack Patterns — Parentheses matching, monotonic stack, histogram, and expression evaluation.
- String Manipulation Patterns — Palindrome checking, anagram detection, pattern matching, and string conversion.
- Heap (Priority Queue) Patterns — Top K elements, K-way merge, two heaps for median, and scheduling.
- Greedy Patterns — Interval scheduling, jump games, stock trading, and task scheduling.
Where to go next
Lowest Common Ancestor (LCA) Finding is one lesson in a 16-pattern DSA course. If you are preparing end to end, work the interview-critical patterns first and use the pattern sheet as the checklist; if you are here for one technique, the Tree Traversal Patterns (DFS & BFS) guide is the shortest path back to the rest of it.