/// <summary>
 /// 求解
 /// </summary>
 /// <returns></returns>
 public Path resolve()
 {
     Path path = new Path();
       Node start = new Node(p.Start);
       LinkedList<Node> Open = new LinkedList<Node>();
       HashSet <Node>Open2=new HashSet<Node> ();  // 元素与Open一样。效率不同。
       HashSet<Node> Close = new HashSet<Node>();
       Open.AddFirst(start);  // 起始点。
       Open2.Add(start);
       bool flag = false;
       Node curr=null;
       while(Open .Count >0)
       {
       curr = Open.First();  // 取出第一个。
       Open.RemoveFirst();
       Open2.Remove (curr);
       Close.Add(curr);     // 放入闭集合,后面会做重复性检查。
       if (curr.cell.End)
       {
           flag = true;
           break;
       }
       curr.Expand(Open, Open2, Close); //展开此节点:其所有的不在Open和Close的子节点,加入到队列尾部。
       }
       if (flag)
       {
      while(curr.Parent !=null)//记录下所有的结果。
      {
          path.cells.Add(curr.cell);
          curr = curr.Parent;
      }
      path.cells.Add(curr.cell);//这是第一个点。
       }
       return path;
 }
        public Path resolve(int pdepth)
        {
            Path path = new Path();

            Node start = new Node(p.Start);
            start.Depth = 0;
            LinkedList<Node> Open = new LinkedList<Node>();
            HashSet<Node> Open2 = new HashSet<Node>();
            HashSet<Node> Close = new HashSet<Node>();
            Open.AddFirst(start);
            Open2.Add(start);
            bool flag = false;
            Node curr = null;
            while (Open.Count > 0)
            {
                curr = Open.First();
                Open.RemoveFirst();
                Open2.Remove(curr);
                Close.Add(curr);
                if (curr.cell.End)
                {
                    flag = true;
                    break;
                }
                if(curr.Depth < pdepth )
                curr.ExpandDF(Open, Open2, Close);
            }
            if (flag)
            {
                while (curr.Parent != null)
                {
                    path.cells.Add(curr.cell);
                    curr = curr.Parent;
                }
                path.cells.Add(curr.cell);
            }
            else
                ;

            return path;
        }
 private void 深度优先ToolStripMenuItem_Click(object sender, EventArgs e)
 {
     if (p.Start == null)
     {
         MessageBox.Show("请输入起点");
         return;
     }
     if (p.End == null)
     {
         MessageBox.Show("请输入终点");
         return;
     }
     DF df = new DF(p);
     path = df.resolve(depth);
     if (path.cells.Count > 0)
         path.Draw();
     else MessageBox.Show("无法到达");
 }