c# - 如何过滤树结构？

Question

我有一棵对象树MyNode：

public class MyNode
{
   public int Type { get; set; }
   public List<MyNode> Children { get; set; }
}

MyNode myRootNode;
// initializing a tree structure

所以我需要删除所有节点，除了

1. 具有Type属性的节点等于int myType

2. 在其子节点中包含具有Type属性的任何级别节点的节点等于int myType

我的方式：

bool Filter(MyNode node, MyNode parentNode, int type)
{
   bool isFound = false;

   if (node.Type == type)
      isFound = true; // There's type

   foreach (MyNode child in node.Children)
   {
      if (FilterTree(child, node, type))
          isFound = true; // There is child node who has this type
   }

   // If there aren't this type neither any of its children has it
   if (!isFound)
   {
      parentNode.Children.Remove(node);
   }

   return isFound;
}

我有一个例外：Collection was modified; enumeration operation may not execute.我认为那是因为我删除了列表中的元素。有没有办法以正确的方式做到这一点？或者我做错了什么？

Answer 1

假设始终保留根节点，您可以删除方法中的子节点，而不是节点本身。

bool Filter(MyNode node,int type)
{
//remove children
foreach(MyNode child in node.Children.Where(c=>!Filter(c, type)).ToArray())
    node.Children.Remove(child);
//return if should be retained
return node.Type==type || node.Children.Count>0;
}

Answer 2

Linq 来拯救你：

public static void RemoveNodesRecursive(this MyNode node, Predicate<MyNode> predicate)
{
    node.Children.RemoveAll(predicate);
    foreach (var n in node.Children)
    {
        RemoveNodes(n);
    }
}

然后从根节点开始：

myRootNode.RemoveNodesRecursive(n => n.node.Type == myType)