Leetcode 529. Minesweeper

Simulate a Minesweeper click on an m×n board: clicking a mine turns it to 'X', while clicking an empty square requires counting adjacent mines — if the count > 0 set the cell to that digit, otherwise mark it 'B' and recursively reveal all neighbors. The core challenge is a grid flood-fill with adjacency counting (use DFS/BFS) to propagate reveals.