How deep does this tree go?

Nested comment threads, category menus and file explorers all arrive as trees, and the first question is usually how deep they go: how far to indent, when to collapse, whether to warn that a reply is nested too far.

Implement maxDepth(node). A node is a plain object shaped { id, children } where children is an array of nodes; the children property may be missing entirely, which means the node has no children. Return the number of levels in the tree: 0 for null, 1 for a node with no children, and one more than the deepest child otherwise.

What it has to do

• Return 0 when the node is null.
• Return 1 for a leaf node, whether children is missing or an empty array.
• Follow the deepest branch, not the first one.
• Handle trees of any depth.

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