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Grokking the Coding Interview Patterns in JavaScript

Solution: Lowest Common Ancestor of a Binary Tree III

Explore how to find the lowest common ancestor of two nodes in a binary tree when only parent pointers are given. Learn a two-pointer method that moves up the tree from both nodes until they meet, ensuring an efficient O(h) time and constant space solution.

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Statement

You are given two nodes, p and q. The task is to return their lowest common ancestor (LCA). Both nodes have a reference to their parent node. The tree’s root is not provided; you must use the parent pointers to find the nodes’ common ancestor.

Note: The lowest common ancestor of two nodes, p and q, is the lowest node in the binary tree, with both p and q as descendants.

In a tree, a descendant of a node is any node reachable by following edges downward from that node, including the node itself. ...