276. Unflatten Object

Convert a flat object with dot-separated paths into a nested object.

Implement:

function unflattenObject(flatObj) {}

Behavior:

• Dot notation creates nested objects ({"a.b": 1} => { a: { b: 1 } })
• Plain keys stay at root
• If a non-object blocks a path, replace it with an object to continue nesting
• Return {} for invalid non-object input

Examples

unflattenObject({
  'user.name': 'Sam',
  'user.age': 20,
});
// { user: { name: 'Sam', age: 20 } }

unflattenObject({
  a: 1,
  'config.theme.color': 'blue',
});
// { a: 1, config: { theme: { color: 'blue' } } }