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 Google phone screen problems in FastPrep.

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FastPrep tags this as a Google phone screen coding practice problem when the problem catalog has that company and stage context.

Lowest Common Ancestor in a Binary Tree

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Problem statement

You are given the root of a binary tree with unique integer values and two values p and q that occur in the tree.

Return the value of their lowest common ancestor: the deepest node whose subtree contains both target nodes. A node is considered an ancestor of itself.

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

Nodes 5 and 1 lie in different subtrees of the root.

Example 2

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

Node 5 is an ancestor of node 4 and may be the answer itself.

Example 3

root = [1,2]p = 1q = 2return = 1

The root is one of the targets.

Constraints

The tree contains between 2 and 2000 nodes.
All node values are unique signed 32-bit integers.
p != q, and both values occur in the tree.