Simulate bubble elimination and maximize common prefix

You are given **two independent coding tasks** (as in a multi-question OA). Solve each. ## Task A — Grid “bubble/candy” elimination simulation You are given an `m x n` grid `board` of integers. Repeatedly apply the following steps until the board becomes stable (no more eliminations): 1. **Mark for elimination**: Any cell that is part of a **horizontal or vertical** run of **3 or more equal values** is marked. - Marking is done based on the board state at the start of the round (i.e., all eliminations in a round happen simultaneously). 2. **Eliminate**: Set all marked cells to `0`. 3. **Gravity**: For each column independently, let all **non-zero** values “fall” toward the bottom, preserving their relative order, and fill the remaining cells at the top with `0` (equivalently: “zeros float up”). **Output:** Return the final stable grid. **Assumptions/constraints (typical OA):** - `1 <= m, n <= 50` (or similar) - Cell values are non-negative integers; `0` represents empty. --- ## Task B — Maximum longest common prefix length from two lists You are given two lists of strings: `A` and `B`. Choose **one** string `a` from `A` and **one** string `b` from `B`. Let `lcp(a, b)` be the length of the **longest common prefix** between `a` and `b`. **Output:** Return the **maximum** possible value of `lcp(a, b)` over all pairs `(a, b)`. **Constraints (to rule out brute force):** - `|A|` and `|B|` can be large (e.g., up to `1e5` total strings) - Total length of all strings can be large (e.g., up to `1e6`) - Lowercase English letters (or ASCII) for simplicity Your solution should be efficient enough that checking all pairs is too slow.