Implement stack variants and upward path sum

Answer the following coding questions. 1. **MinStack**: Design a stack that supports `push(x)`, `pop()`, `top()`, and `getMin()` such that each operation runs in **O(1)** time. 2. **MaxStack**: Design a stack that supports `push(x)`, `pop()`, `top()`, and `getMax()` such that each operation runs in **O(1)** time. 3. **Median of a data stream**: Design a data structure that processes a stream of numbers and supports: - `addNum(x)`: insert a new number - `findMedian()`: return the current median Aim for efficient online updates. 4. **Binary tree upward path sum**: Given the root of a binary tree and a target sum, determine whether there exists a path whose values sum to the target, where the path: - may start at **any node**, - moves **only upward** toward ancestors, - contains one or more nodes, - and cannot revisit nodes. Return `true` if such a path exists, otherwise `false`.