LeetCode "Surrounded Regions"

Flood-Fill. BFS. But there's a trick. If we fill surrounded region directly, extra bookkeeping cost is needed - because we don't know whether that region should be filled or not; but one thing is sure: all regions starting from edges must be the same.

class Solution {
public:
    struct Loc
    {
        Loc(int rx, int ry)
        {
            x = rx; y = ry;
        }
        int x;
        int y;
    };

    bool isOut(int x, int y, int width, int height)
    {
        if (x < 0 || x >= width) return true;
        if (y < 0 || y >= height) return true;
        return false;
    }

    void goSeed(vector<vector<char>> &board, int x, int y, int width, int height)
    {
        queue<Loc> q; q.push(Loc(x, y));
        while (!q.empty())
        {
            int x0 = q.front().x;
            int y0 = q.front().y;
            
            if (!isOut(x0 - 1, y0, width, height) && board[y0][x0 - 1] == 'O')
            {
                q.push(Loc(x0 - 1, y0));
                board[y0][x0 - 1] = '-';
            }
            if (!isOut(x0 + 1, y0, width, height) && board[y0][x0 + 1] == 'O')
            {
                q.push(Loc(x0 + 1, y0));
                board[y0][x0 + 1] = '-';
            }
            if (!isOut(x0, y0 - 1, width, height) && board[y0 - 1][x0] == 'O')
            {
                q.push(Loc(x0, y0 - 1));
                board[y0 - 1][x0] = '-';
            }
            if (!isOut(x0, y0 + 1, width, height) && board[y0 + 1][x0] == 'O')
            {
                q.push(Loc(x0, y0 + 1));
                board[y0 + 1][x0] = '-';
            }
            board[y0][x0] = '-';
            q.pop();
        }
    }

    void solve(vector<vector<char>> &board) {
        if (board.empty()) return;

        int height = board.size();
        int width = board[0].size();
        
        //    Check borders
        for (int i = 0; i < width; i++)
        {
            if (board[0][i] == 'O')    goSeed(board, i, 0, width, height);
            if (board[height - 1][i] == 'O')    goSeed(board, i, height - 1, width, height);
        }
        for (int i = 1; i < height - 1; i++)
        {
            if (board[i][0] == 'O') goSeed(board, 0, i, width, height);
            if (board[i][width - 1] == 'O') goSeed(board, width - 1, i, width, height);
        }

        //    
        for (int i = 0; i < height; i++)
        for (int j = 0; j < width; j++)
        {
            if (board[i][j] == '-') board[i][j] = 'O';
            else if (board[i][j] == 'O') board[i][j] = 'X';
        }

    }
};