Solve remembered OA coding tasks

The online assessment reportedly had five coding questions, but only the following three were described clearly enough to reconstruct: 1. **Find the top three companies by average stock price** You are given a mapping from company name to a list of its daily stock prices over several days. Compute the average stock price for each company and return the names of the **three companies with the highest average price**. If there are fewer than three companies, return all of them. If two companies have the same average, break ties by company name in ascending lexicographic order. 2. **Compute the bounding rectangle of a set of points** You are given a list of 2D coordinates `[(x1, y1), (x2, y2), ..., (xn, yn)]`. Return four values: - the minimum `x` value, - the minimum `y` value, - `max_x - min_x`, - `max_y - min_y`. In other words, return the lower-left corner, width, and height of the smallest axis-aligned rectangle that contains all points. 3. **Validate a partially filled 9x9 number board** You are given a 9x9 grid where each cell contains either a digit `'1'` through `'9'` or `'.'` for empty. Determine whether the current board state is valid under these rules: - no digit may appear more than once in any row, - no digit may appear more than once in any column, - no digit may appear more than once in any 3x3 subgrid. The other two OA questions were not described clearly enough to reconstruct.