I am using c# and List collection and loaded the values. Once it is done I am trying to read them recursively but some how I am not able to achieve this.
the following is my main code.
private static void Main(string[] args)
{
var node = new Node
{
Name = "N1",
Nodes =
new List<Node>
{
new Node { Name = "N1a" },
new Node { Name = "N1b", Nodes = new List<Node> { new Node { Name = "N1B1" } } },
new Node
{
Name = "N1c",
Nodes =
new List<Node> { new Node { Name = "N1C1", Nodes = new List<Node> {new Node{Name = "N1C1A"} } } }
}
}
};
GetNodes( node );
Console.ReadLine();
}
public class Node
{
public string Name { get; set; }
public IList<Node> Nodes { get; set; }
}
and the function call is following
public static IEnumerable<Node> GetNodes(Node node)
{
if (node == null)
{
return null;
}
Console.WriteLine(node.Name);
foreach (var n in node.Nodes)
{
return GetNodes(n);
}
return null;
}
}
Could any one please help me to fix the recursive function?
If you just want to print the names of all the nodes,
public static void GetNodes(Node node)
{
if (node == null)
{
return;
}
Console.WriteLine(node.Name);
foreach (var n in node.Nodes)
{
GetNodes(n);
}
}
If you want to flatten the tree,
public static IEnumerable<Node> GetNodes(Node node)
{
if (node == null)
{
yield break;
}
yield return node;
foreach (var n in node.Nodes)
{
foreach(var innerN in GetNodes(n))
{
yield return innerN;
}
}
}
public static IEnumerable<Node> GetNodes(Node node)
{
if (node == null) return null;
var nodes = new List<Node>();
nodes.Add(node);
Console.WriteLine(node.Name);
if (node.Nodes != null)
{
foreach (var n in node.Nodes)
{
nodes.AddRange(GetNodes(n));
}
}
return nodes;
}}
Your method only every returns null, or calls itself and then either returns null, or calls itself..... so at the end of the day it returns null or doesn't terminate. If you want to seralize the values you can write them into a list at the same point in the code as you write them to the console.
public static void GetNodes(Node node, List<Node> output)
{
if (node == null)
return;
output.Add(node);
Console.WriteLine(node.Name);
foreach (var n in node.Nodes)
{
GetNodes(n, output);
}
}
You return from your method inside a loop immediately, on teh first iteration. No other iterations is performed.
Related
The problem goes like this:
We have a tree that is built using the class Node where an instance of the class represents a node in the tree. For simplicity, the node has a single data field of type int.
Your task is to write the extension method NodeExtensions.Next() to find the next element in the tree. You can write as many helper methods as you want, but don't change the signature of the extension method NodeExtensions.Next().
I have this Node class:
public class Node
{
private List<Node> _children;
public Node(int data, params Node[] nodes)
{
Data = data;
AddRange(nodes);
}
public Node Parent { get; set; }
public IEnumerable<Node> Children
{
get
{
return _children != null
? _children
: Enumerable.Empty<Node>();
}
}
public int Data { get; private set; }
public void Add(Node node)
{
Debug.Assert(node.Parent == null);
if (_children == null)
{
_children = new List<Node>();
}
_children.Add(node);
node.Parent = this;
}
public void AddRange(IEnumerable<Node> nodes)
{
foreach (var node in nodes)
{
Add(node);
}
}
public override string ToString()
{
return Data.ToString();
}
}
The solution should be a extension method such as this
public static Node Next(this Node node)
{
}
The code I tried:
public static Node Next(this Node node)
{
var newNode = NextLargerElement(node, node.Data);
return newNode;
}
public static Node res;
public static Node NextLargerElementUtil(Node root, int x)
{
if (root == null)
return null;
if (root.Data > x)
if ((res == null || (res).Data > root.Data))
res = root;
foreach (var children in root.Children)
{
NextLargerElementUtil(children, x);
}
return res;
}
static Node NextLargerElement(Node root, int x)
{
res = null;
NextLargerElementUtil(root, x);
return res;
}
Here is a testing case:
[Test]
public void Test()
{
// Test tree:
//
// 1
// +-2
// +-3
// +-4
// +-5
// +-6
// +-7
//
var root = new Node(
1,
new Node(
2,
new Node(3),
new Node(4)),
new Node(
5,
new Node(6),
new Node(7)));
// Expected output:
//
// 1
// 2
// 3
// 4
// 5
// 6
// 7
//
var n = root;
while (n != null)
{
Console.WriteLine(n.Data);
n = n.Next();
}
// Test
//
n = root;
Assert.AreEqual(1, n.Data);
n = n.Next();
Assert.AreEqual(2, n.Data);
n = n.Next();
Assert.AreEqual(3, n.Data);
n = n.Next();
Assert.AreEqual(4, n.Data);
n = n.Next();
Assert.AreEqual(5, n.Data);
n = n.Next();
Assert.AreEqual(6, n.Data);
n = n.Next();
Assert.AreEqual(7, n.Data);
n = n.Next();
Assert.IsNull(n);
}
You can use Equals to backtrack your current node position in the tree and return it's parent's next child, if any, if there is not one then you need to backtrack the current node parent position and so on:
public static Node Next(this Node node)
{
if(node.Children != null && node.Children.Any())
{
return node.Children.First();
}
// "backtracking", also can be done recursively
var parent = node.Parent;
while(parent != null)
{
var returnNext = false; // return next element in Children if current is node
foreach (var element in parent.Children)
{
if(returnNext)
{
return element;
}
if(element == node)
{
returnNext = true;
node = parent; // to find parent's position if there is no next child
}
}
parent = parent.Parent;
}
return null;
}
I'm making a program that prints out all Nodes in a Collatz tree in C#.
This takes up a whole lot of memory, and outOfMemoryExceptions have been the word of the day. The base of the program is as follows:
var fileStream = File.Create("collatz.txt"); //just print into a textfile for testing
var writer = new StreamWriter(fileStream);
IEnumerable<Node> nodeList = new List<Node>()
{
new Node(1, null) //rootNode
};
Task flushTask = Task.CompletedTask;
while (nodeList.Any())
{
var tempList = CalcChildren(nodeList); //Return a IEnumerable of children of all the parents in the nodeList
await flushTask;
foreach (var node in tempList)
writer.WriteLine($"{node.Value} -> {node.Parent.Value}: {node.StepsFromRoot}");
flushTask = writer.FlushAsync();
nodeList = tempList;
}
writer.Close();
static IEnumerable<Node> CalcChildren(IEnumerable<Node> parents)
{
foreach(var parent in parents)
foreach (var child in CalcChildren(parent))
yield return child;
}
static IEnumerable<Node> CalcChildren(Node parent)
{
var multiValue = parent.CalcMultiplicationValue();
if (multiValue.HasValue)
{
var child = new Node(multiValue.Value, parent);
parent.MultiplicationChild = child;
yield return child;
}
var divValue = parent.CalcDivisionValue();
if (divValue.HasValue && divValue.Value!=1)
{
var child = new Node(divValue.Value, parent);
parent.DivisionChild = child;
yield return child;
}
}
I think herein lies the problem but for the sake of completeness, the Node class:
public class Node
{
public Node(int value, Node parent)
{
Value = value;
Parent = parent;
if (parent != null)
StepsFromRoot = parent.StepsFromRoot+1;
else
StepsFromRoot = 0;
}
public int Value { get; }
public Node Parent { get; set; }
public Node DivisionChild { get; set; }
public Node MultiplicationChild { get; set; }
public int StepsFromRoot { get; set; }
public int? CalcMultiplicationValue()
{
if(Value<=int.MaxValue/2)
return 2 * Value;
return null;
}
public int? CalcDivisionValue()
{
double newValue = (Value - 1) / 3.0;
if (newValue % 2 == 1 && newValue >= 1)
return (int)newValue;
return null;
}
}
I'm trying my best to drop as much memory as possible, but it doesn't seem to work. Around the 105th iteration this program takes up 4 GB of memory! I first thought it was because the buffer of my writer was taking up all the memory. Now I think it's because the collection of nodes isn't cleaned up by the garbage collector.
I tried to make it more minimal. But I'm not sure what to delete while keeping it complete. Thanks in advance!
I reading hierarchical data into a recursive data structure.
public class Items
{
public string Name { get; set; }
public List<Items> Children { get; set; }
}
So its similar to a tree. My problem is, I have no idea how I can loop over all elements or find a inner element with a specific Name. Since it can be very complex/deep I can not really work with nested loops since I don't know how deep it will get.
How can I have a loop over all elements in such a structure?
Since you need solution without recursion, here is one:
public Items FindByName(Items root, string targetName)
{
var stack = new Stack<Items>();
stack.Push(root);
Items node;
while (true)
{
node = stack.Pop();
if (node == null)
{
// not found ..
}
if (node.Name == targetName)
{
break;
}
foreach (var child in node.Children)
{
stack.Push(child);
}
}
return node;
}
void RecursiveMethod(Items items)
{
if (items.Children != null)
{
foreach (Items i in items.Children)
{
RecursiveMethod(i);
}
}
if (items.Name == "YourName")
{
// Do your stuff..
}
}
You need some traversal algorithm implementation.
There are several ones, either recursive, or non-recursive. It depends on your particular use-cases, which one to choose.
E.g., a kind of non-recursive, lazy width traversal:
public static class TreeVisitor
{
public static IEnumerable<TNodeType> WidthTraversal<TNodeType>(TNodeType root, Func<TNodeType, IEnumerable<TNodeType>> getChildNodesFunc)
where TNodeType : class
{
if (root == null)
{
throw new ArgumentNullException(nameof(root));
}
if (getChildNodesFunc == null)
{
throw new ArgumentNullException(nameof(getChildNodesFunc));
}
var visited = new HashSet<TNodeType>();
var queue = new Queue<TNodeType>();
yield return root;
visited.Add(root);
queue.Enqueue(root);
while (queue.Count > 0)
{
var parent = queue.Dequeue();
foreach (var child in getChildNodesFunc(parent))
{
if (child == default(TNodeType))
continue;
if (!visited.Contains(child))
{
yield return child;
visited.Add(child);
queue.Enqueue(child);
}
}
}
}
}
Usage:
var rootItem = new Items
{
Name = "Root",
Children = new List<Items>
{
new Items { Name = "Child1" },
new Items { Name = "Child2" },
// etc
}
};
foreach (var item in TreeVisitor.WidthTraversal(rootItem, _ => _.Children))
{
// ...
}
I would do it this way:
class Program
{
static void Main(string[] args)
{
List<Item> items = new List<Item>() { new Item { Name = "Pasta", Children = new List<Item>() { new Item { Name = "Pasta", Children = null } } } };
List<Item> pastas = GetItemsByName(items, "Pasta");
}
private static List<Item> GetItemsByName(List<Item> items, string name)
{
List<Item> found = new List<Item>();
foreach (Item item in items)
{
if (item.Name == name)
{
found.Add(item);
}
if (item.Children != null)
{
found.AddRange(GetItemsByName(item.Children, name));
}
}
return found;
}
}
public class Item
{
public string Name { get; set; }
public List<Item> Children { get; set; }
}
I am making a filtereditems class, that will be displayed as a treeview in WPF. The filtereditems class contains only certain node items from a treeitems class that contain certain criteria. I am able clone all of the tree items and add them to the filtereditems list. From there I find nodes that do not meet the criteria and remove them appropriately. However I have found that using the clones renders me unable to remove these items. Is there something I should know about cloned items and why they can't be removed from my collection?
public class Node: INotifyPropertyChanged, ICloneable
{
public Name { get;set;}
public ID {get;set;}
public ParentNode {get;set;}
public ObservableCollection<Nodes> ChildNodes{get;set;}
public object Clone()
{
Node toReturn = new Node();
toReturn.Name = this.Name;
toReturn.ID = this.ID;
toReturn.ParentNode = this.ParentNode;
foreach (Node child in this.ChildNodes)
{
toReturn.ChildNodes.Add((Node) child.Clone());
}
return toReturn;
}
}
public void filterStart(ChildNodesListViewDataSource _filterStart)
{
if (this.FilterString != null && this.Entity != null)
{
this.TotalItemsNumber = 0;
this.FilterItemsNumber = 0;
this.FilterTreeItems.Clear();
foreach (Node y in TreeItems)
{
this.FilterTreeItems.Add((Node)y.Clone());
foreach (Node x in FilterTreeItems)
{
FilterRoot(x);
}
}
TakeOutTrash();
public bool FilterRoot(Node FilterItems)
{
bool HasMatchingChildren = false;
if (FilterItems.ChildNodes != null || FilterItems.ChildNodes.Count !=0)
{
foreach (Node FilterItemsComponenents in FilterItems.ChildNodes)
{
if (FilterRoot(FilterItemsComponenents))
{
HasMatchingChildren = true;
}
}
}
string NameOfFilterItem = FilterItems.Name.ToUpper();
string FilterStringUpperCase = FilterString.ToUpper();
bool FilterStringCheck = NameOfFilterItem.Contains(FilterStringUpperCase);
if (!FilterStringCheck && !HasMatchingChildren)
{
trimIDs.TrashCan.Add(FilterItems);
return false;
}
else
{
return true;
}
}
public void TakeOutTrash()
{
foreach (Node node in trimIDs.TrashCan)
{
this.FilterTreeItems.Remove(node);
}
}
public class TrimIDs
{
public IList<ComponentNodeViewModel> TrashCan { get; set;}
{
TrashCan = new List<ComponentNodeViewModel>();
}
}
I actually solved my issue by creating another clone method that clones anything Node that is not in the List of Nodes not to clone: (Hope this helps anyone that was in my same predicament).
public object Clone(IList<Node> ListNotToClone)
{
NodetoReturnFiltered = new Node();
toReturnFiltered.Name = this.Name;
toReturnFiltered.ID = this.ID;
toReturnFiltered.ParentNode= this.ParentNode;
foreach (Node child in this.ComponentNodes)
{
if (!ListNotToClone.Contains(child))
{
toReturnFiltered.ComponentNodes.Add((Node)child.Clone(ListNotToClone));
}
}
return toReturnFiltered;
}
I then used this method :
public void TakeOutTrash()
{
foreach (ComponentNodeViewModel root in this.FilterTreeItems)
{
FilterHolder = (ComponentNodeViewModel)root.Clone(trimIDs.TrashCan);
}
}
And passed FilterHolder back into FilterTreeItems in the FilterStart method,
this.FilterTreeItems.Clear();
this.FilterTreeItems.Add(FilterHolder);
I have a Node class in C# with the following properties:
public class Node
{
public int Id {get;set;}
public int? ParentId {get;set;}
public string Label {get;set;}
}
I have a TreeView control which provides the following method to create
a new node:
MyTreeView.CreateNode(key, label);
parent.Nodes.CreateNode(key, label);
If I want to add a new child node I need to use the second method otherwise the first one. Both returns an object of type TreeNode.
How would you create in C# a recursive function to populate the treeview considering that the root nodes have ParentId = null?
This is what I have done so far:
// create a list of root nodes
var roots = myList.Where(x => x.ParentId == null);
// send the roots to a recursive func
foreach(var root in roots)
{
AddNode(null,root,myList);
}
this is my recursive function:
private void AddNode(Node parent, Node current, IList<Node> items)
{
TreeNode treenode = null;
if(parent == null)
{
treenode = mytree.CreateNode(current.Id.ToString(), current.Label);
}else{
var parentnode = mytree.GetNode(parent.Id.ToString());
treenode = parentnode.Nodes.CreateNode(current.Id.ToString(), current.Label);
}
// call the recursion for the children
var children = items.Where(x => x.ParentId == current.Id);
foreach(var child in children)
{
AddNode(current, child, items);
}
}
If your tree view control is derived from System.Windows.Forms.TreeView you can replace
MyTreeView.CreateNode(key, label);
parent.Nodes.CreateNode(key, label);
with
MyTreeView.Nodes.Add(key, label);
parent.Nodes.Add(key, label);
So the call always goes to a Nodes collection which is of type TreeNodeCollection. Instead of your Node object you can now use the Nodes collection as parameter.
var roots = myList.Where(x => x.ParentId == null);
foreach (var root in roots)
{
AddNode(mytree.Nodes, root, myList);
}
private void AddNode(TreeNodeCollection nodes, Node current, IList<Node> items)
{
TreeNode treenode = nodes.Add(current.Id.ToString(), current.Label);
var children = items.Where(x => x.ParentId == current.Id);
foreach (var child in children)
{
AddNode(treenode.Nodes, child, items);
}
}
This has two benefits:
You don't need to lookup the parent each time.
You only have one call (TreeNodeCollection.Add).
However, if you can not access the TreeView.Nodes collection in the AddNode call for each root you will have to check for that at the top of the AddNode method.
var roots = myList.Where(x => x.ParentId == null);
foreach (var root in roots)
{
AddNode(null, root, myList);
}
private void AddNode(TreeNodeCollection nodes, Node current, IList<Node> items)
{
if (nodes == null)
{
nodes = myTree.Nodes;
}
...
}
Try this code:
var lookup = myList.ToLookup(n => n.ParentId.ToString());
Action<IEnumerable<TreeNode>> addChildren = null;
addChildren = tns =>
{
var query =
from tn in tns
from cn in lookup[tn.Name]
select tn.Nodes.CreateNode(cn.Id.ToString(), cn.Label);
var nodes = query.ToArray();
if (nodes.Length > 0)
{
addChildren(nodes);
}
};
addChildren(
lookup[null]
.Select(n =>
MyTreeView.CreateNode(n.Id.ToString(), n.Label)));
I couldn't fully test it, so you might need to change some of the code to make it work, but it should be fairly close.
I'd probably do something like this...
public class Node
{
public int Id { get; set; }
public int? ParentId { get; set; }
public string Label { get; set; }
public Node(int? parentId, int id, string label)
{
ParentId = parentId;
Id = id;
Label = label;
}
}
public class TreeNode : List<TreeNode>
{
public string Key { get; set; }
public string Label { get; set; }
public IEnumerable<TreeNode> Descendants
{
get
{
yield return this;
foreach (var child in this)
{
foreach (var descendant in child.Descendants)
{
yield return descendant;
}
}
}
}
public TreeNode(string key, string label)
{
Key = key;
Label = label;
}
public void CreateNode(int id, string label)
{
Add(new TreeNode(id.ToString(), label));
}
}
public class Tree
{
private TreeNode _root = new TreeNode(null, null);
public Tree(IEnumerable<Node> nodes)
{
nodes.ToList().ForEach(node => CreateNode(node.ParentId, node.Id, node.Label));
}
public void CreateNode(int? parentId, int id, string label)
{
if (parentId == null)
{
_root.CreateNode(id, label);
}
else
{
_root.Descendants.First(x => x.Key == parentId.ToString()).CreateNode(id, label);
}
}
public IEnumerable<TreeNode> Descendants => _root.Descendants;
}
Try this code:
Node{
Id, Label, List<Tree> Children
}
Tree GetTree(id){
var node=new Node();
node.Id=id;
node.Children=new List<Node>();
List<Node> children = db.Nodes.Where(x => x.ParentId==id);
foreach(child in children){
var childTree=GetTree(child.Id);
node.Children.Add(childTree);
}
return node;
}