Difference between revisions of "AVL Tree"
Line 50: | Line 50: | ||
</Delphi> | </Delphi> | ||
− | ==Enumerating all items of | + | ==Enumerating all items of a tree== |
+ | |||
+ | This will enumerate from lowest to highest: | ||
<Delphi> | <Delphi> | ||
Line 62: | Line 64: | ||
end; | end; | ||
</Delphi> | </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. |
Revision as of 03:45, 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 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.