Wishlist: Design and Implement a Shared Wishlist System with Priority Ordering

Question

## Problem

Build a `WishlistSystem` class. Each user can have a wishlist of items with priorities. Wishlists can be shared with other users (read-only access). Implement the following:

```python
class WishlistSystem:
    def add_item(self, user_id: str, item: str, priority: int) -> None: ...
    def remove_item(self, user_id: str, item: str) -> None: ...
    def get_wishlist(self, requestor_id: str, owner_id: str) -> list: ...
    # Returns items sorted by priority desc; raises PermissionError if not shared
    def share_with(self, owner_id: str, target_user_id: str) -> None: ...
    def top_item(self, user_id: str) -> str: ...
```

**Example:**
```
ws = WishlistSystem()
ws.add_item("alice", "Laptop", priority=10)
ws.add_item("alice", "Book",   priority=5)
ws.share_with("alice", "bob")

ws.get_wishlist("bob", "alice")   -> ["Laptop", "Book"]
ws.top_item("alice")              -> "Laptop"
ws.get_wishlist("carol", "alice") -> raises PermissionError
```

## Follow-ups

1. How would you support collaborative wishlists where multiple users can add items?
2. How would you implement a "claimed" status so gift-givers can mark an item as purchased without the owner seeing?
3. What data model would you use to store wishlists in a relational database?
4. How would you handle duplicate item names with different priorities from the same user?

Wishlist: Design and Implement a Shared Wishlist System with Priority Ordering

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