Implement string formatting and request tracking tasks

You are given several small coding tasks. Implement each as described. ## Task A — Convert `snake_case` to `camelCase` Write a function that converts an identifier from `snake_case` to `camelCase`. - Input: a string `s` containing lowercase letters `a-z` and underscores `_`. - Output: the camelCase version. - Rules/edge cases: - Consecutive underscores should be treated as a single word separator (ignore empty parts). - If `s` starts/ends with underscores, ignore those underscores. - The first word remains lowercase; each subsequent word is capitalized. Example: - `"hello_world" -> "helloWorld"` - `"__my__var__name_" -> "myVarName"` ## Task B — Format an integer with thousands separators Write a function that formats a (possibly negative) integer with commas as thousands separators. - Input: an integer `n` (may be large; assume it fits in 64-bit signed integer). - Output: a string representation using commas every 3 digits from the right. Examples: - `123 -> "123"` - `1234 -> "1,234"` - `-12345678 -> "-12,345,678"` ## Task C — Validate an OCR string under 180° rotation An OCR system outputs a string `t` that may contain digits and a few letters. You need to decide whether it can represent an integer between **1 and 200 inclusive** under either normal reading or after a **180-degree rotation**. Define a rotation mapping `rot(c)` for characters; rotation is valid only if every character in the string has a mapping. Rotating a whole string means: 1) reverse the string, and 2) replace each character `c` with `rot(c)`. Return `true` if either: - `t` as-is is a valid base-10 integer in `[1, 200]`, OR - `rotate180(t)` is a valid base-10 integer in `[1, 200]`. Assume the rotation map is provided as a dictionary (examples from the interview note included): - `'6' <-> '9'` - plus any additional pairs given at runtime (e.g., `'h' -> '4'`, `'L' -> '7'`). Characters not in the map are invalid for rotation. Examples (assuming map includes `6<->9`, `0->0`, `1->1`, `8->8`): - `"69"` rotates to `"69"` and is valid (`69` in range) -> `true` - `"201"` is out of range, rotate may or may not help -> depends on mapping -> compute ## Task D — Track request begin/end times and print in a required order You are implementing a `Server` class that receives events for requests. Each request has a unique `requestId`. You must implement two methods: - `begin(requestId, timestamp)` - `end(requestId, timestamp)` ### Part 1 Whenever both timestamps for a request are known, print/log a line: - `requestId begin=<beginTs> end=<endTs>` Assumptions: - Events may arrive out of order (an `end` can arrive before `begin`). - There may be multiple in-flight requests. ### Follow-up Instead of printing immediately when a pair is complete, the server must always print **completed requests in increasing order of end time** (earliest `end` printed first). If multiple have the same end time, break ties by `requestId`. Design the data structures and logic to support this ordering efficiently.