public partial class Form1 : Form 
 { 
   public Form1() 
   { 
     InitializeComponent(); 
   } 
  
   private void Form1_Paint(object sender, PaintEventArgs e) 
   { 
     int gridSize = 20; 
     for (int i = 0; i * gridSize  < ClientSize.Width; i++) 
     { 
       e.Graphics.DrawString(i.ToString("00"), Font, Brushes.Black, 
         i * gridSize - 5, 0); 
       e.Graphics.DrawLine(Pens.Gray, i * gridSize, gridSize, 
         i * gridSize, ClientSize.Height); 
     } 
     for (int i = 0; i * gridSize  < ClientSize.Height; i++) 
     { 
       e.Graphics.DrawString(i.ToString("00"), Font, Brushes.Black, 0, 
         i * gridSize - 5); 
       e.Graphics.DrawLine(Pens.Gray, gridSize, i * gridSize, 
         ClientSize.Width, i * gridSize); 
     } 
  
     for (int i = 0; i  < points.Length; i++) 
       e.Graphics.DrawEllipse(Pens.Red, 
         (points[i].X + 1) * gridSize - 3, (points[i].Y + 1) * gridSize - 3, 
         6, 6); 
  
     for (int i = 0; i  < groups.Count; i++) 
     { 
       int minX = int.MaxValue, minY = int.MaxValue,  
         maxX = int.MinValue, maxY = int.MinValue; 
       for (int j = 0; j  < groups[i].Count; j++) 
       { 
         Point p = groups[i][j]; 
         minX = p.X  < minX ? p.X : minX; 
         minY = p.Y  < minY ? p.Y : minY; 
         maxX = p.X > maxX ? p.X : maxX; 
         maxY = p.Y > maxY ? p.Y : maxY; 
       } 
       Rectangle r = Rectangle.FromLTRB( 
         (minX + 1) * gridSize - 5, (minY + 1) * gridSize - 5, 
         (maxX + 1) * gridSize + 5, (maxY + 1) * gridSize + 5); 
       e.Graphics.DrawRectangle(Pens.Blue, r); 
       e.Graphics.DrawString(i.ToString(), Font, Brushes.Black, r); 
     } 
   } 
  
   private const int pointCount = 100; 
   private Point[] points = new Point[pointCount]; 
   private bool[] scans; // 是否计算过 
   private List <List <Point>> groups = new List <List <Point>>();