AVL Tree
TAVLTree
Implemented in the FCL unit avl_tree. This is the predecessor of TAvgLvlTree.
TAvgLvlTree
The AVL trees - Average Level Trees are sorted self balancing binary trees. Similar to a list like TPFList a TAvgLvlTree can store arbitrary data (Pointer), but contrary to TFPList the tree is always sorted and balanced. Therefore searching is very fast. Features:
- You can define your own compare function or method.
- Searching an item or key takes O(log(n))
- Inserting an item takes O(log(n))
- Deleting an item takes O(log(n))
- Finding the lowest or highest item takes log(n)
- Finding the sucessor or precessor item takes O(log(n))
- Iterating through all items in order takes O(n)
- Enumerators for running from lowest to highest and highest to lowest
- Supports duplicates
- Keeps duplicates order stable.
- It is not thread safe, but it does not use any global variables. So it can be used in threads just like TFPList.
Creating a tree
To create a tree you only need a compare function. The following example demonstrates how to sort TMyData objects via their Filenames:
<Delphi> uses AvgLvlTree; // in package lazutils type
TMyData = class public Filename: string; Content: string; end;
function CompareMyData(Data1, Data2: Pointer): integer; begin
Result:=CompareFilenames(TMyData(d1).Filename,TMyData(d2).Filename);
end;
... var
MyData1: TMyData; Tree: TAvgLvlTree;
begin
Tree:=TAvgLvlTree.Create(@CompareMyData);
MyData1:=TMyData.Create; MyData1.Filename:='SomeFile'; Tree.Add(MyData1);
end; </Delphi>
Enumerating all items of a tree
This will enumerate from lowest to highest:
<Delphi> var
MyData: TMyData;
begin
for Node in Tree do begin MyData:=TMyData(Node.Data); writeln(MyData.Filename); end;
end; </Delphi>
This will enumerate from highest to lowest:
<Delphi> var
MyData: TMyData;
begin
for Node in Tree.GetEnumeratorHighToLow do begin MyData:=TMyData(Node.Data); writeln(MyData.Filename); end;
end; </Delphi>
Searching items
You can search an item with the same key:
<Delphi> Node:=Tree.Find(MyData); </Delphi>
Note: Find will find a node where your compare function returns 0.