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JarviixAll problems

Lowest Common Ancestor of a Binary Tree

Medium

Tree · Binary Tree · DFS~20m

Live AI Interview

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Section 1Understand Problem

Section 01

Understand the problem

Restate the problem precisely. Interviewers reward candidates who pause, define the contract, and name the guarantees before coding.

Problem statement

Given a binary tree, find the lowest common ancestor (LCA) of two given node values `p` and `q` in the tree. According to the definition: the lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself). Return the *value* of the LCA node (instead of the node itself, for unit-test parity).

Example

root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1 → 3

Constraints

2 ≤ tree size ≤ 10⁵ · −10⁹ ≤ Node.val ≤ 10⁹ · All Node.val are unique · p ≠ q, both exist

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AI Review

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