Implement stack variants and path-sum check

## Coding tasks Solve the following algorithmic problems. ### 1) MinStack Design a stack supporting: - `push(x)`, `pop()`, `top()` - `getMin()` returning the minimum element currently in the stack All operations should run in **O(1)** time. ### 2) MaxStack Design a stack supporting: - `push(x)`, `pop()`, `top()` - `peekMax()` returning the maximum element currently in the stack - `popMax()` removing and returning the maximum element (if multiple maxima exist, remove the one closest to the top) State expected time complexities and trade-offs. ### 3) Streaming median (data stream) Given a very large stream of integers, support inserting numbers and querying the **current median** at any time. ### 4) Tree path sum with upward-only path Given a binary tree with **positive integer** node values and an integer `target`, determine whether there exists a **single-direction path that starts at any node and only moves upward to parent nodes** such that the sum of the nodes on that path equals `target`. Return `true/false`. Include any reasonable constraints you assume (e.g., number of nodes, value ranges) and handle edge cases (single node, skewed tree, large target).