{ **********************************************************************
    This file is part of the Free Component Library (FCL)
    Copyright (c) 2008 by Mattias Gaertner
    
    Average Level Tree implementation by Mattias Gaertner

    See the file COPYING.FPC, included in this distribution,
    for details about the copyright.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 **********************************************************************

  Author: Mattias Gaertner

  Abstract:
    TAVLTree is an Average Level binary Tree. This binary tree is always
    balanced, so that inserting, deleting and finding a node is performed in
    O(log(#Nodes)).
}
unit AVL_Tree;

{$ifdef FPC}{$mode objfpc}{$endif}{$H+}

interface

{off $DEFINE MEM_CHECK}

uses
  {$IFDEF MEM_CHECK}MemCheck,{$ENDIF}
  Classes, SysUtils;

type
  TAVLTreeNode = class
  public
    Parent, Left, Right: TAVLTreeNode;
    Balance: integer;
    Data: Pointer;
    procedure Clear;
    function TreeDepth: integer; // longest WAY down. e.g. only one node => 0 !
  end;

  TBaseAVLTreeNodeManager = class
  public
    procedure DisposeNode(ANode: TAVLTreeNode); virtual; abstract;
    function NewNode: TAVLTreeNode; virtual; abstract;
  end;

  TAVLTree = class
  private
    FOnCompare: TListSortCompare;
    FCount: integer;
    nodemgr :  TBaseAVLTreeNodeManager;
    procedure BalanceAfterInsert(ANode: TAVLTreeNode);
    procedure BalanceAfterDelete(ANode: TAVLTreeNode);
    function FindInsertPos(Data: Pointer): TAVLTreeNode;
    procedure SetOnCompare(const AValue: TListSortCompare);
  public
    Root: TAVLTreeNode;
    function Find(Data: Pointer): TAVLTreeNode;
    function FindKey(Key: Pointer;
      OnCompareKeyWithData: TListSortCompare): TAVLTreeNode;
    function FindSuccessor(ANode: TAVLTreeNode): TAVLTreeNode;
    function FindPrecessor(ANode: TAVLTreeNode): TAVLTreeNode;
    function FindLowest: TAVLTreeNode;
    function FindHighest: TAVLTreeNode;
    function FindNearest(Data: Pointer): TAVLTreeNode;
    function FindPointer(Data: Pointer): TAVLTreeNode;
    function FindLeftMost(Data: Pointer): TAVLTreeNode;
    function FindRightMost(Data: Pointer): TAVLTreeNode;
    function FindLeftMostKey(Key: Pointer;
      OnCompareKeyWithData: TListSortCompare): TAVLTreeNode;
    function FindRightMostKey(Key: Pointer;
      OnCompareKeyWithData: TListSortCompare): TAVLTreeNode;
    function FindLeftMostSameKey(ANode: TAVLTreeNode): TAVLTreeNode;
    function FindRightMostSameKey(ANode: TAVLTreeNode): TAVLTreeNode;
    procedure Add(ANode: TAVLTreeNode);
    function Add(Data: Pointer): TAVLTreeNode;
    procedure Delete(ANode: TAVLTreeNode);
    procedure Remove(Data: Pointer);
    procedure RemovePointer(Data: Pointer);
    procedure MoveDataLeftMost(var ANode: TAVLTreeNode);
    procedure MoveDataRightMost(var ANode: TAVLTreeNode);
    property OnCompare: TListSortCompare read FOnCompare write SetOnCompare;
    procedure Clear;
    procedure FreeAndClear;
    procedure FreeAndDelete(ANode: TAVLTreeNode);
    property Count: integer read FCount;
    function ConsistencyCheck: integer;
    procedure WriteReportToStream(s: TStream; var StreamSize: int64);
    function ReportAsString: string;
    procedure SetNodeManager(newmgr:TBaseAVLTreeNodeManager);
    constructor Create(OnCompareMethod: TListSortCompare);
    constructor Create;
    destructor Destroy; override;
  end;

  TAVLTreeNodeMemManager = class(TBaseAVLTreeNodeManager)
  private
    FFirstFree: TAVLTreeNode;
    FFreeCount: integer;
    FCount: integer;
    FMinFree: integer;
    FMaxFreeRatio: integer;
    procedure SetMaxFreeRatio(NewValue: integer);
    procedure SetMinFree(NewValue: integer);
    procedure DisposeFirstFreeNode;
  public
    procedure DisposeNode(ANode: TAVLTreeNode); override;
    function NewNode: TAVLTreeNode; override;
    property MinimumFreeNode: integer read FMinFree write SetMinFree;
    property MaximumFreeNodeRatio: integer
        read FMaxFreeRatio write SetMaxFreeRatio; // in one eighth steps
    property Count: integer read FCount;
    procedure Clear;
    constructor Create;
    destructor Destroy; override;
  end;


implementation


var NodeMemManager: TAVLTreeNodeMemManager;


function ComparePointer(Data1, Data2: Pointer): integer;
begin
  if Data1>Data2 then Result:=-1
  else if Data1<Data2 then Result:=1
  else Result:=0;
end;

{ TAVLTree }

function TAVLTree.Add(Data: Pointer): TAVLTreeNode;
begin
  Result:=NodeMgr.NewNode;
  Result.Data:=Data;
  Add(Result);
end;

procedure TAVLTree.Add(ANode: TAVLTreeNode);
// add a node. If there are already nodes with the same value it will be
// inserted rightmost
var InsertPos: TAVLTreeNode;
  InsertComp: integer;
begin
  ANode.Left:=nil;
  ANode.Right:=nil;
  inc(FCount);
  if Root<>nil then begin
    InsertPos:=FindInsertPos(ANode.Data);
    InsertComp:=fOnCompare(ANode.Data,InsertPos.Data);
    ANode.Parent:=InsertPos;
    if InsertComp<0 then begin
      // insert to the left
      InsertPos.Left:=ANode;
    end else begin
      // insert to the right
      InsertPos.Right:=ANode;
    end;
    BalanceAfterInsert(ANode);
  end else begin
    Root:=ANode;
    ANode.Parent:=nil;
  end;
end;

function TAVLTree.FindLowest: TAVLTreeNode;
begin
  Result:=Root;
  if Result<>nil then
    while Result.Left<>nil do Result:=Result.Left;
end;

function TAVLTree.FindHighest: TAVLTreeNode;
begin
  Result:=Root;
  if Result<>nil then
    while Result.Right<>nil do Result:=Result.Right;
end;

procedure TAVLTree.BalanceAfterDelete(ANode: TAVLTreeNode);
var OldParent, OldRight, OldRightLeft, OldLeft, OldLeftRight,
  OldRightLeftLeft, OldRightLeftRight, OldLeftRightLeft, OldLeftRightRight
  : TAVLTreeNode;
begin
  if (ANode=nil) then exit;
  if ((ANode.Balance=+1) or (ANode.Balance=-1)) then exit;
  OldParent:=ANode.Parent;
  if (ANode.Balance=0) then begin
    // Treeheight has decreased by one
    if (OldParent<>nil) then begin
      if(OldParent.Left=ANode) then
        Inc(OldParent.Balance)
      else
        Dec(OldParent.Balance);
      BalanceAfterDelete(OldParent);
    end;
    exit;
  end;
  if (ANode.Balance=+2) then begin
    // Node is overweighted to the right
    OldRight:=ANode.Right;
    if (OldRight.Balance>=0) then begin
      // OldRight.Balance=={0 or -1}
      // rotate left
      OldRightLeft:=OldRight.Left;
      if (OldParent<>nil) then begin
        if (OldParent.Left=ANode) then
          OldParent.Left:=OldRight
        else
          OldParent.Right:=OldRight;
      end else
        Root:=OldRight;
      ANode.Parent:=OldRight;
      ANode.Right:=OldRightLeft;
      OldRight.Parent:=OldParent;
      OldRight.Left:=ANode;
      if (OldRightLeft<>nil) then
        OldRightLeft.Parent:=ANode;
      ANode.Balance:=(1-OldRight.Balance);
      Dec(OldRight.Balance);
      BalanceAfterDelete(OldRight);
    end else begin
      // OldRight.Balance=-1
      // double rotate right left
      OldRightLeft:=OldRight.Left;
      OldRightLeftLeft:=OldRightLeft.Left;
      OldRightLeftRight:=OldRightLeft.Right;
      if (OldParent<>nil) then begin
        if (OldParent.Left=ANode) then
          OldParent.Left:=OldRightLeft
        else
          OldParent.Right:=OldRightLeft;
      end else
        Root:=OldRightLeft;
      ANode.Parent:=OldRightLeft;
      ANode.Right:=OldRightLeftLeft;
      OldRight.Parent:=OldRightLeft;
      OldRight.Left:=OldRightLeftRight;
      OldRightLeft.Parent:=OldParent;
      OldRightLeft.Left:=ANode;
      OldRightLeft.Right:=OldRight;
      if (OldRightLeftLeft<>nil) then
        OldRightLeftLeft.Parent:=ANode;
      if (OldRightLeftRight<>nil) then
        OldRightLeftRight.Parent:=OldRight;
      if (OldRightLeft.Balance<=0) then
        ANode.Balance:=0
      else
        ANode.Balance:=-1;
      if (OldRightLeft.Balance>=0) then
        OldRight.Balance:=0
      else
        OldRight.Balance:=+1;
      OldRightLeft.Balance:=0;
      BalanceAfterDelete(OldRightLeft);
    end;
  end else begin
    // Node.Balance=-2
    // Node is overweighted to the left
    OldLeft:=ANode.Left;
    if (OldLeft.Balance<=0) then begin
      // rotate right
      OldLeftRight:=OldLeft.Right;
      if (OldParent<>nil) then begin
        if (OldParent.Left=ANode) then
          OldParent.Left:=OldLeft
        else
          OldParent.Right:=OldLeft;
      end else
        Root:=OldLeft;
      ANode.Parent:=OldLeft;
      ANode.Left:=OldLeftRight;
      OldLeft.Parent:=OldParent;
      OldLeft.Right:=ANode;
      if (OldLeftRight<>nil) then
        OldLeftRight.Parent:=ANode;
      ANode.Balance:=(-1-OldLeft.Balance);
      Inc(OldLeft.Balance);
      BalanceAfterDelete(OldLeft);
    end else begin
      // OldLeft.Balance = 1
      // double rotate left right
      OldLeftRight:=OldLeft.Right;
      OldLeftRightLeft:=OldLeftRight.Left;
      OldLeftRightRight:=OldLeftRight.Right;
      if (OldParent<>nil) then begin
        if (OldParent.Left=ANode) then
          OldParent.Left:=OldLeftRight
        else
          OldParent.Right:=OldLeftRight;
      end else
        Root:=OldLeftRight;
      ANode.Parent:=OldLeftRight;
      ANode.Left:=OldLeftRightRight;
      OldLeft.Parent:=OldLeftRight;
      OldLeft.Right:=OldLeftRightLeft;
      OldLeftRight.Parent:=OldParent;
      OldLeftRight.Left:=OldLeft;
      OldLeftRight.Right:=ANode;
      if (OldLeftRightLeft<>nil) then
        OldLeftRightLeft.Parent:=OldLeft;
      if (OldLeftRightRight<>nil) then
        OldLeftRightRight.Parent:=ANode;
      if (OldLeftRight.Balance>=0) then
        ANode.Balance:=0
      else
        ANode.Balance:=+1;
      if (OldLeftRight.Balance<=0) then
        OldLeft.Balance:=0
      else
        OldLeft.Balance:=-1;
      OldLeftRight.Balance:=0;
      BalanceAfterDelete(OldLeftRight);
    end;
  end;
end;

procedure TAVLTree.BalanceAfterInsert(ANode: TAVLTreeNode);
var OldParent, OldParentParent, OldRight, OldRightLeft, OldRightRight, OldLeft,
   OldLeftLeft, OldLeftRight: TAVLTreeNode;
begin
  OldParent:=ANode.Parent;
  if (OldParent=nil) then exit;
  if (OldParent.Left=ANode) then begin
    // Node is left son
    dec(OldParent.Balance);
    if (OldParent.Balance=0) then exit;
    if (OldParent.Balance=-1) then begin
      BalanceAfterInsert(OldParent);
      exit;
    end;
    // OldParent.Balance=-2
    if (ANode.Balance=-1) then begin
      // rotate
      OldRight:=ANode.Right;
      OldParentParent:=OldParent.Parent;
      if (OldParentParent<>nil) then begin
        // OldParent has GrandParent. GrandParent gets new child
        if (OldParentParent.Left=OldParent) then
          OldParentParent.Left:=ANode
        else
          OldParentParent.Right:=ANode;
      end else begin
        // OldParent was root node. New root node
        Root:=ANode;
      end;
      ANode.Parent:=OldParentParent;
      ANode.Right:=OldParent;
      OldParent.Parent:=ANode;
      OldParent.Left:=OldRight;
      if (OldRight<>nil) then
        OldRight.Parent:=OldParent;
      ANode.Balance:=0;
      OldParent.Balance:=0;
    end else begin
      // Node.Balance = +1
      // double rotate
      OldParentParent:=OldParent.Parent;
      OldRight:=ANode.Right;
      OldRightLeft:=OldRight.Left;
      OldRightRight:=OldRight.Right;
      if (OldParentParent<>nil) then begin
        // OldParent has GrandParent. GrandParent gets new child
        if (OldParentParent.Left=OldParent) then
          OldParentParent.Left:=OldRight
        else
          OldParentParent.Right:=OldRight;
      end else begin
        // OldParent was root node. new root node
        Root:=OldRight;
      end;
      OldRight.Parent:=OldParentParent;
      OldRight.Left:=ANode;
      OldRight.Right:=OldParent;
      ANode.Parent:=OldRight;
      ANode.Right:=OldRightLeft;
      OldParent.Parent:=OldRight;
      OldParent.Left:=OldRightRight;
      if (OldRightLeft<>nil) then
        OldRightLeft.Parent:=ANode;
      if (OldRightRight<>nil) then
        OldRightRight.Parent:=OldParent;
      if (OldRight.Balance<=0) then
        ANode.Balance:=0
      else
        ANode.Balance:=-1;
      if (OldRight.Balance=-1) then
        OldParent.Balance:=1
      else
        OldParent.Balance:=0;
      OldRight.Balance:=0;
    end;
  end else begin
    // Node is right son
    Inc(OldParent.Balance);
    if (OldParent.Balance=0) then exit;
    if (OldParent.Balance=+1) then begin
      BalanceAfterInsert(OldParent);
      exit;
    end;
    // OldParent.Balance = +2
    if(ANode.Balance=+1) then begin
      // rotate
      OldLeft:=ANode.Left;
      OldParentParent:=OldParent.Parent;
      if (OldParentParent<>nil) then begin
        // Parent has GrandParent . GrandParent gets new child
        if(OldParentParent.Left=OldParent) then
          OldParentParent.Left:=ANode
        else
          OldParentParent.Right:=ANode;
      end else begin
        // OldParent was root node . new root node
        Root:=ANode;
      end;
      ANode.Parent:=OldParentParent;
      ANode.Left:=OldParent;
      OldParent.Parent:=ANode;
      OldParent.Right:=OldLeft;
      if (OldLeft<>nil) then
        OldLeft.Parent:=OldParent;
      ANode.Balance:=0;
      OldParent.Balance:=0;
    end else begin
      // Node.Balance = -1
      // double rotate
      OldLeft:=ANode.Left;
      OldParentParent:=OldParent.Parent;
      OldLeftLeft:=OldLeft.Left;
      OldLeftRight:=OldLeft.Right;
      if (OldParentParent<>nil) then begin
        // OldParent has GrandParent . GrandParent gets new child
        if (OldParentParent.Left=OldParent) then
          OldParentParent.Left:=OldLeft
        else
          OldParentParent.Right:=OldLeft;
      end else begin
        // OldParent was root node . new root node
        Root:=OldLeft;
      end;
      OldLeft.Parent:=OldParentParent;
      OldLeft.Left:=OldParent;
      OldLeft.Right:=ANode;
      ANode.Parent:=OldLeft;
      ANode.Left:=OldLeftRight;
      OldParent.Parent:=OldLeft;
      OldParent.Right:=OldLeftLeft;
      if (OldLeftLeft<>nil) then
        OldLeftLeft.Parent:=OldParent;
      if (OldLeftRight<>nil) then
        OldLeftRight.Parent:=ANode;
      if (OldLeft.Balance>=0) then
        ANode.Balance:=0
      else
        ANode.Balance:=+1;
      if (OldLeft.Balance=+1) then
        OldParent.Balance:=-1
      else
        OldParent.Balance:=0;
      OldLeft.Balance:=0;
    end;
  end;
end;

procedure TAVLTree.Clear;

  procedure DeleteNode(ANode: TAVLTreeNode);
  begin
    if ANode<>nil then begin
      if ANode.Left<>nil then DeleteNode(ANode.Left);
      if ANode.Right<>nil then DeleteNode(ANode.Right);
    end;
    NodeMgr.DisposeNode(ANode);
  end;

// Clear
begin
  DeleteNode(Root);
  Root:=nil;
  FCount:=0;
end;

constructor TAVLTree.Create(OnCompareMethod: TListSortCompare);
begin
  inherited Create;
  nodemgr:=NodeMemManager;
  FOnCompare:=OnCompareMethod;
  FCount:=0;
end;

constructor TAVLTree.Create;
begin
  Create(@ComparePointer);
end;

procedure TAVLTree.Delete(ANode: TAVLTreeNode);
var OldParent, OldLeft, OldRight, Successor, OldSuccParent, OldSuccLeft,
  OldSuccRight: TAVLTreeNode;
  OldBalance: integer;
begin
  OldParent:=ANode.Parent;
  OldBalance:=ANode.Balance;
  ANode.Parent:=nil;
  ANode.Balance:=0;
  if ((ANode.Left=nil) and (ANode.Right=nil)) then begin
    // Node is Leaf (no children)
    if (OldParent<>nil) then begin
      // Node has parent
      if (OldParent.Left=ANode) then begin
        // Node is left Son of OldParent
        OldParent.Left:=nil;
        Inc(OldParent.Balance);
      end else begin
        // Node is right Son of OldParent
        OldParent.Right:=nil;
        Dec(OldParent.Balance);
      end;
      BalanceAfterDelete(OldParent);
    end else begin
      // Node is the only node of tree
      Root:=nil;
    end;
    dec(FCount);
    NodeMgr.DisposeNode(ANode);
    exit;
  end;
  if (ANode.Right=nil) then begin
    // Left is only son
    // and because DelNode is AVL, Right has no childrens
    // replace DelNode with Left
    OldLeft:=ANode.Left;
    ANode.Left:=nil;
    OldLeft.Parent:=OldParent;
    if (OldParent<>nil) then begin
      if (OldParent.Left=ANode) then begin
        OldParent.Left:=OldLeft;
        Inc(OldParent.Balance);
      end else begin
        OldParent.Right:=OldLeft;
        Dec(OldParent.Balance);
      end;
      BalanceAfterDelete(OldParent);
    end else begin
      Root:=OldLeft;
    end;
    dec(FCount);
    NodeMgr.DisposeNode(ANode);
    exit;
  end;
  if (ANode.Left=nil) then begin
    // Right is only son
    // and because DelNode is AVL, Left has no childrens
    // replace DelNode with Right
    OldRight:=ANode.Right;
    ANode.Right:=nil;
    OldRight.Parent:=OldParent;
    if (OldParent<>nil) then begin
      if (OldParent.Left=ANode) then begin
        OldParent.Left:=OldRight;
        Inc(OldParent.Balance);
      end else begin
        OldParent.Right:=OldRight;
        Dec(OldParent.Balance);
      end;
      BalanceAfterDelete(OldParent);
    end else begin
      Root:=OldRight;
    end;
    dec(FCount);
    NodeMgr.DisposeNode(ANode);
    exit;
  end;
  // DelNode has both: Left and Right
  // Replace ANode with symmetric Successor
  Successor:=FindSuccessor(ANode);
  OldLeft:=ANode.Left;
  OldRight:=ANode.Right;
  OldSuccParent:=Successor.Parent;
  OldSuccLeft:=Successor.Left;
  OldSuccRight:=Successor.Right;
  ANode.Balance:=Successor.Balance;
  Successor.Balance:=OldBalance;
  if (OldSuccParent<>ANode) then begin
    // at least one node between ANode and Successor
    ANode.Parent:=Successor.Parent;
    if (OldSuccParent.Left=Successor) then
      OldSuccParent.Left:=ANode
    else
      OldSuccParent.Right:=ANode;
    Successor.Right:=OldRight;
    OldRight.Parent:=Successor;
  end else begin
    // Successor is right son of ANode
    ANode.Parent:=Successor;
    Successor.Right:=ANode;
  end;
  Successor.Left:=OldLeft;
  if OldLeft<>nil then
    OldLeft.Parent:=Successor;
  Successor.Parent:=OldParent;
  ANode.Left:=OldSuccLeft;
  if ANode.Left<>nil then
    ANode.Left.Parent:=ANode;
  ANode.Right:=OldSuccRight;
  if ANode.Right<>nil then
    ANode.Right.Parent:=ANode;
  if (OldParent<>nil) then begin
    if (OldParent.Left=ANode) then
      OldParent.Left:=Successor
    else
      OldParent.Right:=Successor;
  end else
    Root:=Successor;
  // delete Node as usual
  Delete(ANode);
end;

procedure TAVLTree.Remove(Data: Pointer);
var ANode: TAVLTreeNode;
begin
  ANode:=Find(Data);
  if ANode<>nil then
    Delete(ANode);
end;

procedure TAVLTree.RemovePointer(Data: Pointer);
var
  ANode: TAVLTreeNode;
begin
  ANode:=FindPointer(Data);
  if ANode<>nil then
    Delete(ANode);
end;

destructor TAVLTree.Destroy;
begin
  Clear;
  inherited Destroy;
end;

function TAVLTree.Find(Data: Pointer): TAVLTreeNode;
var Comp: integer;
begin
  Result:=Root;
  while (Result<>nil) do begin
    Comp:=fOnCompare(Data,Result.Data);
    if Comp=0 then exit;
    if Comp<0 then begin
      Result:=Result.Left
    end else begin
      Result:=Result.Right
    end;
  end;
end;

function TAVLTree.FindKey(Key: Pointer; OnCompareKeyWithData: TListSortCompare
  ): TAVLTreeNode;
var Comp: integer;
begin
  Result:=Root;
  while (Result<>nil) do begin
    Comp:=OnCompareKeyWithData(Key,Result.Data);
    if Comp=0 then exit;
    if Comp<0 then begin
      Result:=Result.Left
    end else begin
      Result:=Result.Right
    end;
  end;
end;

function TAVLTree.FindLeftMostKey(Key: Pointer;
  OnCompareKeyWithData: TListSortCompare): TAVLTreeNode;
begin
  Result:=FindLeftMostSameKey(FindKey(Key,OnCompareKeyWithData));
end;

function TAVLTree.FindRightMostKey(Key: Pointer;
  OnCompareKeyWithData: TListSortCompare): TAVLTreeNode;
begin
  Result:=FindRightMostSameKey(FindKey(Key,OnCompareKeyWithData));
end;

function TAVLTree.FindLeftMostSameKey(ANode: TAVLTreeNode): TAVLTreeNode;
var
  LeftNode: TAVLTreeNode;
  Data: Pointer;
begin
  if ANode<>nil then begin
    Data:=ANode.Data;
    Result:=ANode;
    repeat
      LeftNode:=FindPrecessor(Result);
      if (LeftNode=nil) or (fOnCompare(Data,LeftNode.Data)<>0) then break;
      Result:=LeftNode;
    until false;
  end else begin
    Result:=nil;
  end;
end;

function TAVLTree.FindRightMostSameKey(ANode: TAVLTreeNode): TAVLTreeNode;
var
  RightNode: TAVLTreeNode;
  Data: Pointer;
begin
  if ANode<>nil then begin
    Data:=ANode.Data;
    Result:=ANode;
    repeat
      RightNode:=FindSuccessor(Result);
      if (RightNode=nil) or (fOnCompare(Data,RightNode.Data)<>0) then break;
      Result:=RightNode;
    until false;
  end else begin
    Result:=nil;
  end;
end;

function TAVLTree.FindNearest(Data: Pointer): TAVLTreeNode;
var Comp: integer;
begin
  Result:=Root;
  while (Result<>nil) do begin
    Comp:=fOnCompare(Data,Result.Data);
    if Comp=0 then exit;
    if Comp<0 then begin
      if Result.Left<>nil then
        Result:=Result.Left
      else
        exit;
    end else begin
      if Result.Right<>nil then
        Result:=Result.Right
      else
        exit;
    end;
  end;
end;

function TAVLTree.FindPointer(Data: Pointer): TAVLTreeNode;
begin
  Result:=FindLeftMost(Data);
  while (Result<>nil) do begin
    if Result.Data=Data then break;
    Result:=FindSuccessor(Result);
    if fOnCompare(Data,Result.Data)<>0 then Result:=nil;
  end;
end;

function TAVLTree.FindLeftMost(Data: Pointer): TAVLTreeNode;
var
  Left: TAVLTreeNode;
begin
  Result:=Find(Data);
  while (Result<>nil) do begin
    Left:=FindPrecessor(Result);
    if (Left=nil) or (fOnCompare(Data,Left.Data)<>0) then break;
    Result:=Left;
  end;
end;

function TAVLTree.FindRightMost(Data: Pointer): TAVLTreeNode;
var
  Right: TAVLTreeNode;
begin
  Result:=Find(Data);
  while (Result<>nil) do begin
    Right:=FindSuccessor(Result);
    if (Right=nil) or (fOnCompare(Data,Right.Data)<>0) then break;
    Result:=Right;
  end;
end;

function TAVLTree.FindInsertPos(Data: Pointer): TAVLTreeNode;
var Comp: integer;
begin
  Result:=Root;
  while (Result<>nil) do begin
    Comp:=fOnCompare(Data,Result.Data);
    if Comp<0 then begin
      if Result.Left<>nil then
        Result:=Result.Left
      else
        exit;
    end else begin
      if Result.Right<>nil then
        Result:=Result.Right
      else
        exit;
    end;
  end;
end;

function TAVLTree.FindSuccessor(ANode: TAVLTreeNode): TAVLTreeNode;
begin
  Result:=ANode.Right;
  if Result<>nil then begin
    while (Result.Left<>nil) do Result:=Result.Left;
  end else begin
    Result:=ANode;
    while (Result.Parent<>nil) and (Result.Parent.Right=Result) do
      Result:=Result.Parent;
    Result:=Result.Parent;
  end;
end;

function TAVLTree.FindPrecessor(ANode: TAVLTreeNode): TAVLTreeNode;
begin
  Result:=ANode.Left;
  if Result<>nil then begin
    while (Result.Right<>nil) do Result:=Result.Right;
  end else begin
    Result:=ANode;
    while (Result.Parent<>nil) and (Result.Parent.Left=Result) do
      Result:=Result.Parent;
    Result:=Result.Parent;
  end;
end;

procedure TAVLTree.MoveDataLeftMost(var ANode: TAVLTreeNode);
var LeftMost, PreNode: TAVLTreeNode;
  Data: Pointer;
begin
  if ANode=nil then exit;
  LeftMost:=ANode;
  repeat
    PreNode:=FindPrecessor(LeftMost);
    if (PreNode=nil) or (FOnCompare(ANode,PreNode)<>0) then break;
    LeftMost:=PreNode;
  until false;
  if LeftMost=ANode then exit;
  Data:=LeftMost.Data;
  LeftMost.Data:=ANode.Data;
  ANode.Data:=Data;
  ANode:=LeftMost;
end;

procedure TAVLTree.MoveDataRightMost(var ANode: TAVLTreeNode);
var RightMost, PostNode: TAVLTreeNode;
  Data: Pointer;
begin
  if ANode=nil then exit;
  RightMost:=ANode;
  repeat
    PostNode:=FindSuccessor(RightMost);
    if (PostNode=nil) or (FOnCompare(ANode,PostNode)<>0) then break;
    RightMost:=PostNode;
  until false;
  if RightMost=ANode then exit;
  Data:=RightMost.Data;
  RightMost.Data:=ANode.Data;
  ANode.Data:=Data;
  ANode:=RightMost;
end;

function TAVLTree.ConsistencyCheck: integer;
var RealCount: integer;

  function CheckNode(ANode: TAVLTreeNode): integer;
  var LeftDepth, RightDepth: integer;
  begin
    if ANode=nil then begin
      Result:=0;
      exit;
    end;
    inc(RealCount);
    // test left son
    if ANode.Left<>nil then begin
      if ANode.Left.Parent<>ANode then begin
        Result:=-2;  exit;
      end;
      if fOnCompare(ANode.Left.Data,ANode.Data)>0 then begin
        //DebugLn('CCC-3 ',HexStr(PtrInt(ANode.Data),8),' ',HexStr(PtrInt(ANode.Left.Data),8));
        Result:=-3;  exit;
      end;
      Result:=CheckNode(ANode.Left);
      if Result<>0 then exit;
    end;
    // test right son
    if ANode.Right<>nil then begin
      if ANode.Right.Parent<>ANode then begin
        Result:=-4;  exit;
      end;
      if fOnCompare(ANode.Data,ANode.Right.Data)>0 then begin
        //DebugLn('CCC-5 ',HexStr(PtrInt(ANode.Data),8),' ',HexStr(PtrInt(ANode.Right.Data),8));
        Result:=-5;  exit;
      end;
      Result:=CheckNode(ANode.Right);
      if Result<>0 then exit;
    end;
    // test balance
    if ANode.Left<>nil then
      LeftDepth:=ANode.Left.TreeDepth+1
    else
      LeftDepth:=0;
    if ANode.Right<>nil then
      RightDepth:=ANode.Right.TreeDepth+1
    else
      RightDepth:=0;
    if ANode.Balance<>(RightDepth-LeftDepth) then begin
      Result:=-6;  exit;
    end;
    // ok
    Result:=0;
  end;

// TAVLTree.ConsistencyCheck
begin
  RealCount:=0;
  Result:=CheckNode(Root);
  if Result<>0 then exit;
  if FCount<>RealCount then begin
    Result:=-1;
    exit;
  end;
end;

procedure TAVLTree.FreeAndClear;

  procedure FreeNode(ANode: TAVLTreeNode);
  begin
    if ANode=nil then exit;
    FreeNode(ANode.Left);
    FreeNode(ANode.Right);
    if ANode.Data<>nil then TObject(ANode.Data).Free;
    ANode.Data:=nil;
  end;

// TAVLTree.FreeAndClear
begin
  // free all data
  FreeNode(Root);
  // free all nodes
  Clear;
end;

procedure TAVLTree.FreeAndDelete(ANode: TAVLTreeNode);
var OldData: TObject;
begin
  OldData:=TObject(ANode.Data);
  Delete(ANode);
  OldData.Free;
end;

procedure TAVLTree.WriteReportToStream(s: TStream; var StreamSize: int64);
var h: string;

  procedure WriteStr(const Txt: string);
  begin
    if s<>nil then
      s.Write(Txt[1],length(Txt));
    inc(StreamSize,length(Txt));
  end;

  procedure WriteTreeNode(ANode: TAVLTreeNode; const Prefix: string);
  var b: string;
  begin
    if ANode=nil then exit;
    WriteTreeNode(ANode.Right,Prefix+'  ');
    b:=Prefix+HexStr(PtrInt(ANode.Data),8)+'    '
        +'  Self='+HexStr(PtrInt(ANode),8)
        +'  Parent='+HexStr(PtrInt(ANode.Parent),8)
        +'  Balance='+IntToStr(ANode.Balance)
        +#13#10;
    WriteStr(b);
    WriteTreeNode(ANode.Left,Prefix+'  ');
  end;

// TAVLTree.WriteReportToStream
begin
  h:='Consistency: '+IntToStr(ConsistencyCheck)+' ---------------------'+#13#10;
  WriteStr(h);
  WriteTreeNode(Root,'  ');
  h:='-End-Of-AVL-Tree---------------------'+#13#10;
  WriteStr(h);
end;

function TAVLTree.ReportAsString: string;
var ms: TMemoryStream;
  StreamSize: int64;
begin
  Result:='';
  ms:=TMemoryStream.Create;
  try
    StreamSize:=0;
    WriteReportToStream(nil,StreamSize);
    ms.Size:=StreamSize;
    StreamSize:=0;
    WriteReportToStream(ms,StreamSize);
    StreamSize:=0;
    if StreamSize>0 then begin
      ms.Position:=0;
      SetLength(Result,StreamSize);
      ms.Read(Result[1],StreamSize);
    end;
  finally
    ms.Free;
  end;
end;

procedure TAVLTree.SetOnCompare(const AValue: TListSortCompare);
var List: PPointer;
  ANode: TAVLTreeNode;
  i, OldCount: integer;
begin
  if FOnCompare=AValue then exit;
  // sort the tree again
  if Count>0 then begin
    OldCount:=Count;
    GetMem(List,SizeOf(Pointer)*OldCount);
    try
      // save the data in a list
      ANode:=FindLowest;
      i:=0;
      while ANode<>nil do begin
        List[i]:=ANode.Data;
        inc(i);
        ANode:=FindSuccessor(ANode);
      end;
      // clear the tree
      Clear;
      // set the new compare function
      FOnCompare:=AValue;
      // re-add all nodes
      for i:=0 to OldCount-1 do
        Add(List[i]);
    finally
      FreeMem(List);
    end;
  end else
    FOnCompare:=AValue;
end;

procedure TAVLTree.SetNodeManager(newmgr:TBaseAVLTreeNodeManager);
// only allowed just after create.
begin
 nodemgr:=newmgr;
end;

{ TAVLTreeNode }

function TAVLTreeNode.TreeDepth: integer;
// longest WAY down. e.g. only one node => 0 !
var LeftDepth, RightDepth: integer;
begin
  if Left<>nil then
    LeftDepth:=Left.TreeDepth+1
  else
    LeftDepth:=0;
  if Right<>nil then
    RightDepth:=Right.TreeDepth+1
  else
    RightDepth:=0;
  if LeftDepth>RightDepth then
    Result:=LeftDepth
  else
    Result:=RightDepth;
end;

procedure TAVLTreeNode.Clear;
begin
  Parent:=nil;
  Left:=nil;
  Right:=nil;
  Balance:=0;
  Data:=nil;
end;



{ TAVLTreeNodeMemManager }

constructor TAVLTreeNodeMemManager.Create;
begin
  inherited Create;
  FFirstFree:=nil;
  FFreeCount:=0;
  FCount:=0;
  FMinFree:=100;
  FMaxFreeRatio:=8; // 1:1
end;

destructor TAVLTreeNodeMemManager.Destroy;
begin
  Clear;
  inherited Destroy;
end;

procedure TAVLTreeNodeMemManager.DisposeNode(ANode: TAVLTreeNode);
begin
  if ANode=nil then exit;
  if (FFreeCount<FMinFree) or (FFreeCount<((FCount shr 3)*FMaxFreeRatio)) then
  begin
    // add ANode to Free list
    ANode.Clear;
    ANode.Right:=FFirstFree;
    FFirstFree:=ANode;
    inc(FFreeCount);
    if (FFreeCount>(((8+FMaxFreeRatio)*FCount) shr 3)) then begin
      DisposeFirstFreeNode;
      DisposeFirstFreeNode;
    end;
  end else begin
    // free list full -> free the ANode
    ANode.Free;
  end;
  dec(FCount);
end;

function TAVLTreeNodeMemManager.NewNode: TAVLTreeNode;
begin
  if FFirstFree<>nil then begin
    // take from free list
    Result:=FFirstFree;
    FFirstFree:=FFirstFree.Right;
    Result.Right:=nil;
  end else begin
    // free list empty -> create new node
    Result:=TAVLTreeNode.Create;
  end;
  inc(FCount);
end;

procedure TAVLTreeNodeMemManager.Clear;
var ANode: TAVLTreeNode;
begin
  while FFirstFree<>nil do begin
    ANode:=FFirstFree;
    FFirstFree:=FFirstFree.Right;
    ANode.Right:=nil;
    ANode.Free;
  end;
  FFreeCount:=0;
end;

procedure TAVLTreeNodeMemManager.SetMaxFreeRatio(NewValue: integer);
begin
  if NewValue<0 then NewValue:=0;
  if NewValue=FMaxFreeRatio then exit;
  FMaxFreeRatio:=NewValue;
end;

procedure TAVLTreeNodeMemManager.SetMinFree(NewValue: integer);
begin
  if NewValue<0 then NewValue:=0;
  if NewValue=FMinFree then exit;
  FMinFree:=NewValue;
end;

procedure TAVLTreeNodeMemManager.DisposeFirstFreeNode;
var OldNode: TAVLTreeNode;
begin
  if FFirstFree=nil then exit;
  OldNode:=FFirstFree;
  FFirstFree:=FFirstFree.Right;
  dec(FFreeCount);
  OldNode.Right:=nil;
  OldNode.Free;
end;


initialization
  NodeMemManager:=TAVLTreeNodeMemManager.Create;

finalization
  NodeMemManager.Free;
  NodeMemManager:=nil;
end.
