Browser Tab History Data Structure

Question

## Problem

Design a structure simulating browser tabs/history: open a tab, close a tab, and go back to the previous page.

## Example
```
open(A), open(B), back() -> A, close()
```

## Constraints
- Up to 10^5 operations

## Approach
Stack(s) for back/forward; discuss the close semantics. Recurring Snowflake question.