Reveal a Minesweeper Region with Adjacent-Mine Counts

## Problem Implement a Minesweeper reveal operation. The board is a rectangular integer matrix with these initial values: - `-1` is a mine. - `0` is an unrevealed non-mine cell. You are also given the row and column of one non-mine cell to reveal. Return the board after applying the rules below: - A revealed cell with one or more adjacent mines becomes that mine count, from `1` through `8`. - A revealed cell with no adjacent mines becomes `-2`. - When a revealed cell has no adjacent mines, reveal each of its adjacent unrevealed non-mine cells by the same rules. - Do not expand recursively from a numbered cell. - Mines and non-reached cells keep their original values. The eight cells that share an edge or corner are considered adjacent. ### Function Contract Write `revealMinesweeper(board, row, col)` and return the fully updated matrix. You may update `board` in place before returning it. ### Constraints & Assumptions - `1 <= rows, columns` and `rows * columns <= 100,000`. - Every row has the same number of columns. - Every initial cell is either `-1` or `0`. - `(row, col)` is in bounds and identifies a `0`, never a mine. - A mine count is always computed from the original mine locations; revealing cells never changes mine locations. - Each reachable cell should be processed at most once. ### Clarifying Questions to Ask - Do diagonal mines count? For this exercise, all eight neighboring positions count. - What represents a revealed zero-mine cell? Use `-2`, because `0` remains the unrevealed marker. - Should the reveal continue through numbered cells? No. Reveal the numbered boundary cell, but continue traversal only from a cell whose adjacent-mine count is zero. - May the input matrix be mutated? Yes, provided the returned matrix is the final board. ### Part 1 — Reveal One Cell First handle the local rule. Count mines around the selected cell. If the count is positive, store that number and stop. If it is zero, store `-2` and make the cell eligible for expansion. ```hint Separate counting from traversal Use a fixed list of eight direction offsets. A helper that counts in-bounds neighboring mines keeps the local rule consistent during the later traversal. ``` #### What This Part Should Cover - Correct boundary checks for corners and edges. - Counts only `-1` cells, including diagonal mines. - Writes a positive count for a numbered cell and `-2` for a revealed zero-mine cell. - Does not overwrite a mine or an unrelated unrevealed cell. ### Part 2 — Reveal the Connected Empty Region Extend the operation with DFS or BFS. Whenever a processed non-mine cell has zero adjacent mines, visit its unrevealed non-mine neighbors. Numbered neighbors are revealed but do not generate further expansion. ```hint Mark before adding work Change a zero-mine cell to `-2` before pushing its neighbors. The board itself can then serve as the visited set and prevent the same cell from being scheduled repeatedly. ``` #### What This Part Should Cover - Traversal begins only after the clicked cell is found to have zero adjacent mines. - Every reached `0` is converted either to its positive adjacent-mine count or to `-2`. - Only zero-count cells expand the search frontier. - The implementation handles a large connected empty area without doing repeated work; an iterative traversal avoids call-stack overflow at the stated limit. ### Examples For the input below, revealing `(2, 0)` opens the zero-mine region and its numbered boundary: ```text board = [ [ 0, 0, -1], [ 0, 0, 0], [ 0, 0, 0] ] row = 2, col = 0 result = [ [-2, 1, -1], [-2, 1, 1], [-2, -2, -2] ] ``` If the clicked cell already borders a mine, only that cell is revealed: ```text board = [ [-1, 0], [ 0, 0] ] row = 0, col = 1 result = [ [-1, 1], [ 0, 0] ] ``` ### Evaluation Focus - The returned board follows the exact `-1`, `0`, `-2`, and `1` through `8` state definitions. - The traversal condition is based on both facts from the prompt: the current cell is non-mine and its adjacent-mine count is zero. - Time is `O(rows * columns)` in the worst case and auxiliary space is `O(rows * columns)` for the frontier. ### Extensions to Discuss 1. How would the contract change if clicking a mine were allowed? 2. How would you avoid rescanning all eight neighbors if many reveals were performed on the same fixed board? 3. What additional state would be needed to support flagging cells without confusing flags with revealed counts?