Problem

In a Meta mobile UI hierarchy, each view is a node in a rooted tree. Given the root of the view tree and two target views, return their lowest common ancestor: the deepest view that is an ancestor of both targets.

If either target view does not exist in the tree, return None.

Formal Specification

Implement a function:

• Input: root (root ViewNode), view1 (ViewNode), view2 (ViewNode)
• Output: the ViewNode representing the lowest common ancestor, or None

Each node has:

• id: unique integer identifier
• children: list of child ViewNode objects

Examples

Example 1 Input: tree with 1 -> [2, 3], 2 -> [4, 5], 3 -> [6], view1 = 4, view2 = 5 Output: 2 Explanation: Both views are under node 2, and no deeper common ancestor exists.

Example 2 Input: same tree, view1 = 4, view2 = 6 Output: 1 Explanation: The paths are 1->2->4 and 1->3->6, so the root is their lowest common ancestor.

Constraints

• 1 <= number of views <= 10^5
• Each node has a unique id
• The tree is rooted and acyclic
• view1 and view2 may be the same node
• Either target may be absent from the tree