How should I practice Lowest Common Ancestor in a Binary Tree?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Apple phone screen problems in FastPrep.

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Lowest Common Ancestor in a Binary Tree

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Problem statement

Given a nonempty binary tree with unique node values and two values p and q present in the tree, return the value of their lowest common ancestor.

A node is an ancestor of itself. The lowest common ancestor is the deepest node whose subtree contains both target nodes. The targets may be equal. The tree need not be a binary search tree, and neither input tree links nor values may be changed.

The tree is displayed in level order, with null for missing children.

Function

lowestCommonAncestorValue(root: TreeNode, p: int, q: int) → int

Examples

Example 1

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

The targets occur in different root subtrees.

Example 2

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

The node holding five is itself an ancestor of the node holding four.

Constraints

The valid tree contains between 1 and 20000 nodes.
Node values are unique integers in [-10^9,10^9].
Both p and q are existing node values.