529. Minesweeper

class Solution {
    
    unordered_set<string> visited;
    
    inline string hash(int r, int c) {
        return to_string(r) + "#" + to_string(c);
    }
    
    void check(vector<vector<char>>& board, 
               int row, 
               int col,
               vector<vector<int>>& blocks,
               int& mines) {
        
        int width = board[0].size();
        int height = board.size();
        
        int dirs[] = {
            //left
            -1, 0,
            //right
            1, 0,
            //up
            0, -1,
            //down
            0, 1,
            //topleft
            -1, -1,
            //topright
            1, -1,
            //bottomleft
            -1, 1,
            //bottomright
            1, 1
        };
        
        for (int i = 0; i < 8; ++i) {
            int dr = row + dirs[2*i];
            int dc = col + dirs[2*i + 1];
            if (dr < 0 || dr > height - 1 || dc < 0 || dc > width - 1) {
                continue;
            }
            
            if (board[dr][dc] == 'M') {
                mines++;
            }
            else if (board[dr][dc] == 'E') {
                blocks.push_back({dr, dc});
            }
        }
        
    }
    
    void reveal(vector<vector<char>>& board, int row, int col) {
        auto key = hash(row, col);
        if (visited.find(key) != visited.end()) return;
        visited.insert(key);
        
        vector<vector<int>> blocks;
        int mineCount = 0;
        check(board, row, col, blocks, mineCount);
        
        if (mineCount > 0) {
            board[row][col] = '0' + mineCount;
            return;
        }
        
        board[row][col] = 'B';
        
        for (auto& b : blocks) {
            reveal(board, b[0], b[1]);
        }
    }
public:
    vector<vector<char>> updateBoard(vector<vector<char>>& board, vector<int>& click) {
        int row = click[0];
        int col = click[1];
        
        if (board[row][col] == 'M') {
            board[row][col] = 'X';
            return board;
        }
        
        reveal(board, row, col);
        return board;
    }
};