Rotten oranges

  int orangesRotting(vector<vector<int>>& grid) {
        int m = grid.size() ; 
        int n = grid[0].size() ; 
        vector<vector<int>>  visited ( m , vector <int>(n , 0) ) ; 
        queue <pair < pair <int , int > , int >  >  q; 
    

        for(int i = 0 ; i < grid.size() ; i++)
        {
            for(int j =0 ; j < grid[0].size() ; j++)
            {
                if(grid[i][j] == 2)
                {
                    q.push( {{i , j} , 0}) ; 
                    visited[i][j] = 1 ; 
                }
            }
        }
        int maxmin = 0 ;
        while( !q.empty())
        {
           int i = q.front().first.first ; 
           int j = q.front().first.second ; 
           int min = q.front().second ;
           q.pop() ; 
            int a[4] = {1 , 0 , -1, 0} ; 
         int b[4] = {0 , 1, 0 , -1};
          for(int k = 0 ; k < 4 ; k++)
        {
           
             int x = a[k] ;
             int y = b[k] ; 
           //  cout << i + x << j + y << endl ; 
             if(i + x < m  && j + y < n && i + x >= 0 && j + y >= 0 && visited[i + x][j + y] == 0  && grid[i + x][j + y] == 1)
             {
                  q.push({{i + x , j + y} , min + 1}) ; 
                  maxmin = max(maxmin , min + 1) ;
                  visited[i + x][j + y] = 1; 

             }
         }

        } 

        for(int i = 0 ; i < m ; i++)
        {
            for(int j = 0 ; j < n ; j++)
            {
                if(visited[i][j] == 0 && grid[i][j] == 1)
                {
                    return -1 ; 
                }
            }
        }
        return maxmin ; 
    }