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我試圖實現算法以將有向無環圖轉換爲樹（有趣，學習，kata，將其命名）。於是我拿出數據結構的節點：將有向非循環圖（DAG）轉換爲樹
/// <summary>
/// Represeting a node in DAG or Tree
/// </summary>
/// <typeparam name="T">Value of the node</typeparam>
public class Node<T>
{
/// <summary>
/// creats a node with no child nodes
/// </summary>
/// <param name="value">Value of the node</param>
public Node(T value)
{
Value = value;
ChildNodes = new List<Node<T>>();
}
/// <summary>
/// Creates a node with given value and copy the collection of child nodes
/// </summary>
/// <param name="value">value of the node</param>
/// <param name="childNodes">collection of child nodes</param>
public Node(T value, IEnumerable<Node<T>> childNodes)
{
if (childNodes == null)
{
throw new ArgumentNullException("childNodes");
}
ChildNodes = new List<Node<T>>(childNodes);
Value = value;
}
/// <summary>
/// Determines if the node has any child node
/// </summary>
/// <returns>true if has any</returns>
public bool HasChildNodes
{
get { return this.ChildNodes.Count != 0; }
}
/// <summary>
/// Travearse the Graph recursively
/// </summary>
/// <param name="root">root node</param>
/// <param name="visitor">visitor for each node</param>
public void Traverse(Node<T> root, Action<Node<T>> visitor)
{
if (root == null)
{
throw new ArgumentNullException("root");
}
if (visitor == null)
{
throw new ArgumentNullException("visitor");
}
visitor(root);
foreach (var node in root.ChildNodes)
{
Traverse(node, visitor);
}
}
/// <summary>
/// Value of the node
/// </summary>
public T Value { get; private set; }
/// <summary>
/// List of all child nodes
/// </summary>
public List<Node<T>> ChildNodes { get; private set; }
}
這是非常簡單的。方法：
/// <summary>
/// Helper class for Node
/// </summary>
/// <typeparam name="T">Value of a node</typeparam>
public static class NodeHelper
{
/// <summary>
/// Converts Directed Acyclic Graph to Tree data structure using recursion.
/// </summary>
/// <param name="root">root of DAG</param>
/// <param name="seenNodes">keep track of child elements to find multiple connections (f.e. A connects with B and C and B also connects with C)</param>
/// <returns>root node of the tree</returns>
public static Node<T> DAG2TreeRec<T>(this Node<T> root, HashSet<Node<T>> seenNodes)
{
if (root == null)
{
throw new ArgumentNullException("root");
}
if (seenNodes == null)
{
throw new ArgumentNullException("seenNodes");
}
var length = root.ChildNodes.Count;
for (int i = 0; i < length; ++i)
{
var node = root.ChildNodes[i];
if (seenNodes.Contains(node))
{
var nodeClone = new Node<T>(node.Value, node.ChildNodes);
node = nodeClone;
}
else
{
seenNodes.Add(node);
}
DAG2TreeRec(node, seenNodes);
}
return root;
}
/// <summary>
/// Converts Directed Acyclic Graph to Tree data structure using explicite stack.
/// </summary>
/// <param name="root">root of DAG</param>
/// <param name="seenNodes">keep track of child elements to find multiple connections (f.e. A connects with B and C and B also connects with C)</param>
/// <returns>root node of the tree</returns>
public static Node<T> DAG2Tree<T>(this Node<T> root, HashSet<Node<T>> seenNodes)
{
if (root == null)
{
throw new ArgumentNullException("root");
}
if (seenNodes == null)
{
throw new ArgumentNullException("seenNodes");
}
var stack = new Stack<Node<T>>();
stack.Push(root);
while (stack.Count > 0)
{
var tempNode = stack.Pop();
var length = tempNode.ChildNodes.Count;
for (int i = 0; i < length; ++i)
{
var node = tempNode.ChildNodes[i];
if (seenNodes.Contains(node))
{
var nodeClone = new Node<T>(node.Value, node.ChildNodes);
node = nodeClone;
}
else
{
seenNodes.Add(node);
}
stack.Push(node);
}
}
return root;
}
}
和測試：
static void Main(string[] args)
{
// Jitter preheat
Dag2TreeTest();
Dag2TreeRecTest();
Console.WriteLine("Running time ");
Dag2TreeTest();
Dag2TreeRecTest();
Console.ReadKey();
}
public static void Dag2TreeTest()
{
HashSet<Node<int>> hashSet = new HashSet<Node<int>>();
Node<int> root = BulidDummyDAG();
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
var treeNode = root.DAG2Tree<int>(hashSet);
stopwatch.Stop();
Console.WriteLine(string.Format("Dag 2 Tree = {0}ms",stopwatch.ElapsedMilliseconds));
}
private static Node<int> BulidDummyDAG()
{
Node<int> node2 = new Node<int>(2);
Node<int> node4 = new Node<int>(4);
Node<int> node3 = new Node<int>(3);
Node<int> node5 = new Node<int>(5);
Node<int> node6 = new Node<int>(6);
Node<int> node7 = new Node<int>(7);
Node<int> node8 = new Node<int>(8);
Node<int> node9 = new Node<int>(9);
Node<int> node10 = new Node<int>(10);
Node<int> root = new Node<int>(1);
//making DAG
root.ChildNodes.Add(node2);
root.ChildNodes.Add(node3);
node3.ChildNodes.Add(node2);
node3.ChildNodes.Add(node4);
root.ChildNodes.Add(node5);
node4.ChildNodes.Add(node6);
node4.ChildNodes.Add(node7);
node5.ChildNodes.Add(node8);
node2.ChildNodes.Add(node9);
node9.ChildNodes.Add(node8);
node9.ChildNodes.Add(node10);
var length = 10000;
Node<int> tempRoot = node10;
for (int i = 0; i < length; i++)
{
var nextChildNode = new Node<int>(11 + i);
tempRoot.ChildNodes.Add(nextChildNode);
tempRoot = nextChildNode;
}
return root;
}
public static void Dag2TreeRecTest()
{
HashSet<Node<int>> hashSet = new HashSet<Node<int>>();
Node<int> root = BulidDummyDAG();
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
var treeNode = root.DAG2TreeRec<int>(hashSet);
stopwatch.Stop();
Console.WriteLine(string.Format("Dag 2 Tree Rec = {0}ms",stopwatch.ElapsedMilliseconds));
}
更重要的是，數據結構需要一定的改良效果：
- 重寫GetHash，的toString，平等相待，==操作符
- 實現了IComparable
- LinkedList可能是更好的選擇
另外，在轉換之前有需要進行檢查certian thigs：
- 多重圖
- 如果它是DAG（週期）
- Diamnods在DAG中的DAG
- 多根
總而言之，它縮小到幾個問題： 如何改進轉換？由於這是一個反覆，有可能炸燬堆棧。我可以添加堆棧來記憶它。如果我做延續傳球的風格，我會更有效率嗎？
我覺得在這種情況下不可變的數據結構會更好。這是對的嗎？
Childs是正確的名字嗎？ :)
在回答你的問題'孩子是正確的名字嗎？'，'孩子'是一個更好的名字，甚至是'ChildNodes'。 –
'Children'更好:) – pbalaga
100％確定Children節點在Tree中。圖形（各種）還有childern節點？圖論中的 –