Surrounded Regions

class Solution {
public:
    void bfsBoundary(vector<vector<char> >& board, int w, int l)
    {
        int width = board.size();
        int length = board[0].size();
        deque<pair<int, int> > q;
        q.push_back(make_pair(w, l));
        board[w][l] = ‘B‘;
        while (!q.empty()) {
            pair<int, int> cur = q.front();
            q.pop_front();
            pair<int, int> adjs[4] = {{cur.first-1, cur.second}, 
                {cur.first+1, cur.second}, 
                {cur.first, cur.second-1},
                {cur.first, cur.second+1}};
            for (int i = 0; i < 4; ++i)
            {
                int adjW = adjs[i].first;
                int adjL = adjs[i].second;
                if ((adjW >= 0) && (adjW < width) && (adjL >= 0)
                        && (adjL < length) 
                        && (board[adjW][adjL] == ‘O‘)) {
                    q.push_back(make_pair(adjW, adjL));
                    board[adjW][adjL] = ‘B‘;
                }
            }
        }
    }
    
    void solve(vector<vector<char> > &board) {
        int width = board.size();
        if (width == 0) 
            return;
        int length = board[0].size();
        if  (length == 0) 
            return;
    
        for (int i = 0; i < length; ++i)
        {
            if (board[0][i] == ‘O‘)
                bfsBoundary(board, 0, i);
    
            if (board[width-1][i] == ‘O‘)
                bfsBoundary(board, width-1, i);
        }
    
        for (int i = 0; i < width; ++i)
        {
            if (board[i][0] == ‘O‘)
                bfsBoundary(board, i, 0);
            if (board[i][length-1] == ‘O‘)
                bfsBoundary(board, i, length-1);
        }
    
        for (int i = 0; i < width; ++i)
        {
            for (int j = 0; j < length; ++j)
            {
                if (board[i][j] == ‘O‘)
                    board[i][j] = ‘X‘;
                else if (board[i][j] == ‘B‘)
                    board[i][j] = ‘O‘;
            }
        }
    }
};