Difference between revisions of "AVL Tree"
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To create a tree you only need a compare function. The following example demonstrates how to sort TMyData objects via their Filenames: | To create a tree you only need a compare function. The following example demonstrates how to sort TMyData objects via their Filenames: | ||
− | |||
<Delphi> | <Delphi> | ||
+ | uses AvgLvlTree; // in package lazutils | ||
type | type | ||
TMyData = class | TMyData = class | ||
Line 38: | Line 38: | ||
... | ... | ||
− | Tree:=TAvgLvlTree.Create(@CompareMyData); | + | var |
− | MyData1:=TMyData.Create; | + | MyData1: TMyData; |
− | MyData1.Filename:='SomeFile'; | + | Tree: TAvgLvlTree; |
− | Tree.Add(MyData1); | + | begin |
+ | Tree:=TAvgLvlTree.Create(@CompareMyData); | ||
+ | |||
+ | MyData1:=TMyData.Create; | ||
+ | MyData1.Filename:='SomeFile'; | ||
+ | Tree.Add(MyData1); | ||
+ | end; | ||
+ | </Delphi> | ||
+ | |||
+ | ==Enumerating all items of the tree== | ||
+ | |||
+ | <Delphi> | ||
+ | var | ||
+ | MyData: TMyData; | ||
+ | begin | ||
+ | for Node in Tree do begin | ||
+ | MyData:=TMyData(Node.Data); | ||
+ | writeln(MyData.Filename); | ||
+ | end; | ||
+ | end; | ||
</Delphi> | </Delphi> |
Revision as of 03:41, 18 March 2012
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 the tree
<Delphi> var
MyData: TMyData;
begin
for Node in Tree do begin MyData:=TMyData(Node.Data); writeln(MyData.Filename); end;
end; </Delphi>