构建使用对象列表的树 [英] Building a tree using a list of objects

问题描述

我有物业编号和PARENT_ID对象的列表。
我想建立一个树的孩子和家长联系起来。
1父母可能有几个孩子，有一个对象，这将是所有对象的祖先。

I have a list of objects with property id and parent_id.
I want to build a tree to link up those children and parents.
1 parent may have several children and there is an object which will be the ancestor of all objects.

什么是最快的算法来实现呢？
我使用C＃作为编程语言，但其他语言也没关系。

What's the fastest algorithm to implement that?
I use C# as programming language, but other languages are also okay.

推荐答案

这样的东西应该做的伎俩：

Something like that should do the trick :

public List<Node> MakeTreeFromFlatList(IEnumerable<Node> flatList)
{
    var dic = flatList.ToDictionary(n => n.Id, n => n);
    var rootNodes = new List<Node>();
    foreach(var node in flatList)
    {
        if (node.ParentId.HasValue)
        {
            Node parent = dic[node.ParentId.Value];
            node.Parent = parent;
            parent.Children.Add(node);
        }
        else
        {
            rootNodes.Add(node);
        }
    }
    return rootNodes;
}

（假设的ParentId是可空＆LT; INT＆GT; ，并且是空的根节点）

(assuming that ParentId is a Nullable<int>, and is null for root nodes)

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