Boards and Pins - Design a Pinterest-like Save and Retrieval System

Question

## Round 1 - Coding / OOD

## Problem

Design a system that models Pinterest boards and pins. Users can create boards, add pins to boards, and search pins by keyword.

```python
class Pin:
    def __init__(self, pin_id: int, title: str, url: str, tags: list[str]): ...

class Board:
    def __init__(self, board_id: int, name: str, owner: str): ...
    def add_pin(self, pin: Pin) -> None: ...
    def remove_pin(self, pin_id: int) -> None: ...
    def get_pins(self) -> list[Pin]: ...

class PinSystem:
    def create_board(self, name: str, owner: str) -> Board: ...
    def save_pin(self, board_id: int, pin: Pin) -> None: ...
    def search(self, keyword: str) -> list[Pin]: ...
    def get_boards_for_user(self, user: str) -> list[Board]: ...
```

```
Example:
sys = PinSystem()
b = sys.create_board("Recipes", "alice")
p = Pin(1, "Pasta Carbonara", "http://...", ["pasta", "italian"])
sys.save_pin(b.board_id, p)
sys.search("italian") -> [Pin(1, ...)]
```

## Follow-ups

1. How would you index pins for fast keyword search at millions of pins?
2. A pin can be saved to multiple boards - how does your data model handle this?
3. How would you implement a "recommended pins" feature based on a board's existing pins?
4. How would you paginate results from `get_pins` and `search`?

Boards and Pins - Design a Pinterest-like Save and Retrieval System

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