Solve interval merge and string dedup problems

You are given three coding questions from a phone screen. Solve each independently. ## 1) Merge overlapping intervals **Input:** A list of intervals `intervals`, where each interval is `[start, end]` and `start <= end`. **Task:** Merge all overlapping intervals and return a list of non-overlapping intervals that cover the same ranges. **Output:** The merged intervals, typically sorted by start. **Example:** - Input: `[[1,3],[2,6],[8,10],[15,18]]` - Output: `[[1,6],[8,10],[15,18]]` **Constraints (assume):** - `1 <= n <= 10^5` - Interval endpoints fit in 32-bit signed integers. --- ## 2) Remove adjacent duplicates (pair removal) **Input:** A string `s`. **Task:** Repeatedly remove adjacent duplicate characters when they appear as a pair (e.g., remove "aa"), until no more such pairs exist. **Output:** The final resulting string. **Example:** - Input: `"abbaca"` - Process: `abbaca -> aaca -> ca` - Output: `"ca"` **Constraints (assume):** - `1 <= |s| <= 10^5` - Characters can be treated as ASCII letters/digits. --- ## 3) Remove adjacent duplicates in groups of size k **Input:** A string `s` and an integer `k >= 2`. **Task:** Repeatedly remove any group of **k identical characters that are adjacent**. Continue until no such group exists. **Output:** The final resulting string. **Example:** - Input: `s = "deeedbbcccbdaa", k = 3` - Output: `"aa"` **Constraints (assume):** - `1 <= |s| <= 10^5` - `2 <= k <= 10^5` - Characters can include letters and digits.