Leetcode 130 Solution

class Solution {
    int m;
    int n;
public:
    void mark(vector<vector<char>>& board, int y, int x)
    {
        queue<pair<int, int>> q;

        board[y][x] = 'P';
        q.push(make_pair(y, x));

        while (q.empty() == false)
        {
            auto pair = q.front();
            q.pop();

            int i = pair.first;
            int j = pair.second;

            if (i > 0 && board[i - 1][j] == 'O')
                board[i - 1][j] = 'P', q.push(make_pair(i - 1, j));

            if (i < m - 1 && board[i + 1][j] == 'O')
                board[i + 1][j] = 'P', q.push(make_pair(i + 1, j));

            if (j > 0 && board[i][j - 1] == 'O')
                board[i][j - 1] = 'P', q.push(make_pair(i, j - 1));

            if (j < n - 1 && board[i][j + 1] == 'O')
                board[i][j + 1] = 'P', q.push(make_pair(i, j + 1));
         }
    }

    void solve(vector<vector<char>>& board)
    {
        m = board.size();
        if (m == 0)
            return;
        n = board[0].size();

        for (int i = 0; i < m; i++)
        {
            if (board[i][0] == 'O')
                mark(board, i, 0);

            if (board[i][n - 1] == 'O')
                mark(board, i, n - 1);
        }

        for (int j = 0; j < n; j++)
        {
            if (board[0][j] == 'O')
                mark(board, 0, j);

            if (board[m - 1][j] == 'O')
                mark(board, m - 1, j);
        }

        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                if (board[i][j] == 'O')
                    board[i][j] = 'X';

        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                if (board[i][j] == 'P')
                    board[i][j] = 'O';
    }
};