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Grokking the Coding Interview Patterns in Go

Solution: Lowest Common Ancestor of a Binary Tree III

Explore how to identify the lowest common ancestor of two nodes in a binary tree when only parent pointers are available. Learn to use a two-pointer technique that traverses upward and aligns pointers by switching starting positions, enabling you to efficiently find the common ancestor with constant space and linear time complexity.

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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. ...