12 files changed, 1236 insertions, 2 deletions
diff --git a/Занимательное программирование/7/4_solver/assets/1.slv b/Занимательное программирование/7/4_solver/assets/1.slv
new file mode 100644
index 0000000..9ef8749
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/assets/1.slv
@@ -0,0 +1,6 @@
+xxxxxxxxxxx
+x         x
+x b       x
+x  p sbxx x
+x      x px
+xxxxxxxxxxx
diff --git a/Занимательное программирование/7/4_solver/assets/2.slv b/Занимательное программирование/7/4_solver/assets/2.slv
new file mode 100644
index 0000000..3caee9e
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/assets/2.slv
@@ -0,0 +1,9 @@
+xxxxxxxxx
+x   x   x
+xx x   xx
+x       x
+x p x   x
+x   x   x
+x b x   x
+x s     x
+xxxxxxxxx
diff --git a/Занимательное программирование/7/4_solver/assets/graphics.png b/Занимательное программирование/7/4_solver/assets/graphics.png
new file mode 100644
index 0000000..39b8af1
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/assets/graphics.png
diff --git a/Занимательное программирование/7/4_solver/assets/numbers.png b/Занимательное программирование/7/4_solver/assets/numbers.png
new file mode 100644
index 0000000..e089747
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/assets/numbers.png
diff --git a/Занимательное программирование/7/4_solver/problems.pas b/Занимательное программирование/7/4_solver/problems.pas
new file mode 100644
index 0000000..1046603
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/problems.pas
@@ -0,0 +1,218 @@
+unit Problems;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, States;
+
+function GetNeighbours(AState: TState): TStates;
+function Search(InitialState: TState): TStates;
+{ Можно ли передвинуть камень в указанном направлении. }
+function CanPush(Element, Delta: TPosition; Walls, Boulders: TPositions): Boolean;
+function IsGoal(ANode: TNode): Boolean;
+
+function AtSomePosition(Needle: TPosition; Heap: TPositions): Boolean;
+{ Дистанция между двумя позициями не учитывая стен. }
+function ManhattanDistance(A, B: TPosition): Integer;
+function CalculateHeuristic(AState: TState): Integer;
+function ReconstructPath(CameFrom: TNode): TStates;
+
+implementation
+
+function GetNeighbours(AState: TState): TStates;
+const
+  { Вниз, вверх, вправо, влево. }
+  Moves: array[1..4] of TPosition = (
+    (X: 0; Y: 1),
+    (X: 0; Y: -1),
+    (X: 1; Y: 0),
+    (X: -1; Y: 0)
+  );
+var
+  NewState: TState;
+  NewPosition, Move, Boulder: TPosition;
+begin
+  Result := TStates.Create;
+
+  for Move in Moves do
+  begin
+    NewPosition.X := AState.Agent.X + Move.X;
+    NewPosition.Y := AState.Agent.Y + Move.Y;
+
+    if IsFree(NewPosition, AState.Walls) then
+    begin
+      NewState := TState.Create(AState, NewPosition);
+
+      { Если можно передвинуть камень, добавляем новую позицию камня.
+      Иначе, оставляем камень на месте. }
+      for Boulder in AState.Boulders do
+        if Boulder = NewPosition then
+          if CanPush(Boulder, Move, AState.Walls, AState.Boulders) then
+            NewState.AddBoulder(Boulder.X + Move.X, Boulder.Y + Move.Y)
+          else
+          begin
+            FreeAndNil(NewState);
+            break
+          end
+        else
+          NewState.AddBoulder(Boulder.X, Boulder.Y);
+
+      if NewState <> nil then
+      begin
+        SetLength(Result, Length(Result) + 1);
+        Result[High(Result)] := NewState
+      end
+    end
+  end
+end;
+
+function CanPush(Element, Delta: TPosition; Walls, Boulders: TPositions): Boolean;
+var
+  NewPosition: TPosition;
+begin
+  NewPosition.X := Element.X + Delta.X;
+  NewPosition.Y := Element.Y + Delta.Y;
+  Result := IsFree(NewPosition, Walls) and IsFree(NewPosition, Boulders)
+end;
+
+function IsGoal(ANode: TNode): Boolean;
+var
+  CurrentPlace: TPosition;
+begin
+  Result := true;
+
+  for CurrentPlace in ANode.State.Places do
+  begin
+    Result := AtSomePosition(CurrentPlace, ANode.State.Boulders);
+    if not Result then
+      Exit
+  end
+end;
+
+function Search(InitialState: TState): TStates;
+var
+  Frontier: TPriorityQueue;
+  Heuristics, i: Integer;
+  NextState, CurrentState: TState;
+  NextNode, CurrentNode: TNode;
+  Neighbours: TStates;
+  Visited: TStates;
+begin
+  Visited := TStates.Create;
+  Result := TStates.Create;
+
+  Frontier := TPriorityQueue.Create;
+  try
+    Heuristics := CalculateHeuristic(initialState);
+    { Создаем начало графа. }
+    NextState := TState.Create(InitialState);
+    NextNode := TNode.Create(NextState, nil, 0, Heuristics);
+    Frontier.Add(NextNode);
+
+    while not Frontier.IsEmpty do
+    begin
+      Heuristics := Frontier.Count;
+      CurrentNode := Frontier.Poll;
+
+      SetLength(Visited, Length(Visited) + 1);
+      Visited[High(Visited)] := CurrentNode.State;
+
+      if IsGoal(CurrentNode) then
+      begin
+        Result := ReconstructPath(CurrentNode);
+        Exit
+      end;
+      Neighbours := GetNeighbours(CurrentNode.State);
+
+      for i := 0 to High(Neighbours) do
+      begin
+        NextState := Neighbours[i];
+        for CurrentState in Visited do
+          if CurrentState.Compare(NextState) then
+          begin
+            FreeAndNil(NextState);
+            break
+          end;
+
+        if NextState <> nil then
+        begin
+          Heuristics := CalculateHeuristic(NextState);
+          NextNode := TNode.Create(NextState, CurrentNode, CurrentNode.Cost + 1, Heuristics);
+          Frontier.Add(NextNode)
+        end
+      end
+    end
+  finally
+    FreeAndNil(Frontier)
+  end;
+end;
+
+function AtSomePosition(Needle: TPosition; Heap: TPositions): Boolean;
+var
+  CurrentPosition: TPosition;
+begin
+  Result := false;
+  for CurrentPosition in Heap do
+    if CurrentPosition = Needle then
+    begin
+      Result := true;
+      Exit
+    end
+end;
+
+function ManhattanDistance(A, B: TPosition): Integer;
+begin
+  Result := Abs(A.X - B.X) + Abs(A.Y - B.Y)
+end;
+
+function CalculateHeuristic(AState: TState): Integer;
+var
+  CurrentPlace, CurrentBoulder: TPosition;
+  Distance, MinimalDistance: Integer;
+begin
+  Result := 0;
+  for CurrentBoulder in AState.Boulders do
+  begin
+    MinimalDistance := Integer.MaxValue;
+    for CurrentPlace in AState.Places do
+    begin
+      Distance := ManhattanDistance(CurrentBoulder, CurrentPlace);
+      if (not AtSomePosition(CurrentPlace, AState.Boulders)) and (Distance < MinimalDistance) then
+        MinimalDistance := Distance
+    end;
+    Inc(Result, MinimalDistance)
+  end
+end;
+
+function ReconstructPath(CameFrom: TNode): TStates;
+var
+  Temporary: TState;
+  CurrentLength, CurrentSegment: Integer;
+begin
+  Result := TStates.Create;
+  CurrentLength := 0;
+
+  while CameFrom <> nil do
+  begin
+    SetLength(Result, CurrentLength + 1);
+    Result[CurrentLength] := TState.Create(CameFrom.State);
+    CameFrom := CameFrom.Node;
+    Inc(CurrentLength)
+  end;
+  Dec(CurrentLength);
+  CurrentSegment := 0;
+
+  while CurrentSegment < CurrentLength do
+  begin
+    Temporary := Result[CurrentSegment];
+    Result[CurrentSegment] := Result[CurrentLength];
+    Result[CurrentLength] := Temporary;
+    Dec(CurrentLength);
+    Inc(CurrentSegment)
+  end
+end;
+
+end.
+
diff --git a/Занимательное программирование/7/4_solver/solver.lpi b/Занимательное программирование/7/4_solver/solver.lpi
new file mode 100644
index 0000000..225be54
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/solver.lpi
@@ -0,0 +1,93 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<CONFIG>
+  <ProjectOptions>
+    <Version Value="12"/>
+    <General>
+      <SessionStorage Value="InProjectDir"/>
+      <Title Value="solver"/>
+      <Scaled Value="True"/>
+      <ResourceType Value="res"/>
+      <UseXPManifest Value="True"/>
+      <XPManifest>
+        <DpiAware Value="True"/>
+      </XPManifest>
+      <Icon Value="0"/>
+    </General>
+    <BuildModes>
+      <Item Name="Default" Default="True"/>
+    </BuildModes>
+    <PublishOptions>
+      <Version Value="2"/>
+      <UseFileFilters Value="True"/>
+    </PublishOptions>
+    <RunParams>
+      <FormatVersion Value="2"/>
+    </RunParams>
+    <RequiredPackages>
+      <Item>
+        <PackageName Value="LCL"/>
+      </Item>
+    </RequiredPackages>
+    <Units>
+      <Unit>
+        <Filename Value="solver.lpr"/>
+        <IsPartOfProject Value="True"/>
+      </Unit>
+      <Unit>
+        <Filename Value="unit1.pas"/>
+        <IsPartOfProject Value="True"/>
+        <ComponentName Value="Form1"/>
+        <HasResources Value="True"/>
+        <ResourceBaseClass Value="Form"/>
+        <UnitName Value="Unit1"/>
+      </Unit>
+      <Unit>
+        <Filename Value="state.pas"/>
+        <IsPartOfProject Value="True"/>
+        <UnitName Value="State"/>
+      </Unit>
+      <Unit>
+        <Filename Value="assets/problems.pas"/>
+        <IsPartOfProject Value="True"/>
+        <UnitName Value="Problems"/>
+      </Unit>
+      <Unit>
+        <Filename Value="assets/4.slv"/>
+        <IsPartOfProject Value="True"/>
+      </Unit>
+    </Units>
+  </ProjectOptions>
+  <CompilerOptions>
+    <Version Value="11"/>
+    <Target>
+      <Filename Value="solver"/>
+    </Target>
+    <SearchPaths>
+      <IncludeFiles Value="$(ProjOutDir)"/>
+      <UnitOutputDirectory Value="lib/$(TargetCPU)-$(TargetOS)"/>
+    </SearchPaths>
+    <Linking>
+      <Debugging>
+        <DebugInfoType Value="dsDwarf3"/>
+      </Debugging>
+      <Options>
+        <Win32>
+          <GraphicApplication Value="True"/>
+        </Win32>
+      </Options>
+    </Linking>
+  </CompilerOptions>
+  <Debugging>
+    <Exceptions>
+      <Item>
+        <Name Value="EAbort"/>
+      </Item>
+      <Item>
+        <Name Value="ECodetoolError"/>
+      </Item>
+      <Item>
+        <Name Value="EFOpenError"/>
+      </Item>
+    </Exceptions>
+  </Debugging>
+</CONFIG>
diff --git a/Занимательное программирование/7/4_solver/solver.lpr b/Занимательное программирование/7/4_solver/solver.lpr
new file mode 100644
index 0000000..d5fc39e
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/solver.lpr
@@ -0,0 +1,28 @@
+program solver;
+
+{$mode objfpc}{$H+}
+
+uses
+  {$IFDEF UNIX}
+  cthreads,
+  {$ENDIF}
+  {$IFDEF HASAMIGA}
+  athreads,
+  {$ENDIF}
+  Interfaces, // this includes the LCL widgetset
+  Forms, Unit1, States, Problems
+  { you can add units after this };
+
+{$R *.res}
+
+begin
+  RequireDerivedFormResource:=True;
+  Application.Scaled:=True;
+  {$PUSH}{$WARN 5044 OFF}
+  Application.MainFormOnTaskbar:=True;
+  {$POP}
+  Application.Initialize;
+  Application.CreateForm(TForm1, Form1);
+  Application.Run;
+end.
+
diff --git a/Занимательное программирование/7/4_solver/solver.lps b/Занимательное программирование/7/4_solver/solver.lps
new file mode 100644
index 0000000..043698c
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/solver.lps
@@ -0,0 +1,241 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<CONFIG>
+  <ProjectSession>
+    <Version Value="12"/>
+    <BuildModes Active="Default"/>
+    <Units>
+      <Unit>
+        <Filename Value="solver.lpr"/>
+        <IsPartOfProject Value="True"/>
+        <EditorIndex Value="-1"/>
+        <CursorPos Y="27"/>
+        <UsageCount Value="80"/>
+      </Unit>
+      <Unit>
+        <Filename Value="unit1.pas"/>
+        <IsPartOfProject Value="True"/>
+        <ComponentName Value="Form1"/>
+        <HasResources Value="True"/>
+        <ResourceBaseClass Value="Form"/>
+        <UnitName Value="Unit1"/>
+        <TopLine Value="60"/>
+        <CursorPos Y="73"/>
+        <UsageCount Value="80"/>
+        <Loaded Value="True"/>
+        <LoadedDesigner Value="True"/>
+      </Unit>
+      <Unit>
+        <Filename Value="state.pas"/>
+        <IsPartOfProject Value="True"/>
+        <UnitName Value="State"/>
+        <EditorIndex Value="-1"/>
+        <CursorPos X="8"/>
+        <UsageCount Value="76"/>
+      </Unit>
+      <Unit>
+        <Filename Value="assets/problems.pas"/>
+        <IsPartOfProject Value="True"/>
+        <UnitName Value="Problems"/>
+        <EditorIndex Value="-1"/>
+        <CursorPos X="14"/>
+        <UsageCount Value="51"/>
+      </Unit>
+      <Unit>
+        <Filename Value="assets/1.slv"/>
+        <EditorIndex Value="3"/>
+        <CursorPos X="8" Y="6"/>
+        <UsageCount Value="31"/>
+        <Loaded Value="True"/>
+        <DefaultSyntaxHighlighter Value="None"/>
+      </Unit>
+      <Unit>
+        <Filename Value="states.pas"/>
+        <UnitName Value="States"/>
+        <EditorIndex Value="4"/>
+        <TopLine Value="219"/>
+        <CursorPos X="13" Y="168"/>
+        <UsageCount Value="38"/>
+        <Loaded Value="True"/>
+      </Unit>
+      <Unit>
+        <Filename Value="unit1.lfm"/>
+        <EditorIndex Value="-1"/>
+        <UsageCount Value="5"/>
+        <DefaultSyntaxHighlighter Value="LFM"/>
+      </Unit>
+      <Unit>
+        <Filename Value="assets/2.slv"/>
+        <EditorIndex Value="-1"/>
+        <CursorPos X="14" Y="9"/>
+        <UsageCount Value="20"/>
+        <DefaultSyntaxHighlighter Value="None"/>
+      </Unit>
+      <Unit>
+        <Filename Value="assets/3.slv"/>
+        <EditorIndex Value="-1"/>
+        <UsageCount Value="21"/>
+        <DefaultSyntaxHighlighter Value="None"/>
+      </Unit>
+      <Unit>
+        <Filename Value="../../../../opt/lazarus/fpc/3.2.2/source/rtl/objpas/fgl.pp"/>
+        <EditorIndex Value="1"/>
+        <TopLine Value="891"/>
+        <CursorPos X="5" Y="905"/>
+        <UsageCount Value="20"/>
+        <Loaded Value="True"/>
+      </Unit>
+      <Unit>
+        <Filename Value="problems.pas"/>
+        <UnitName Value="Problems"/>
+        <EditorIndex Value="2"/>
+        <TopLine Value="118"/>
+        <CursorPos X="63" Y="129"/>
+        <UsageCount Value="25"/>
+        <Loaded Value="True"/>
+      </Unit>
+      <Unit>
+        <Filename Value="assets/4.slv"/>
+        <IsPartOfProject Value="True"/>
+        <IsVisibleTab Value="True"/>
+        <EditorIndex Value="5"/>
+        <CursorPos Y="3"/>
+        <UsageCount Value="36"/>
+        <Loaded Value="True"/>
+        <DefaultSyntaxHighlighter Value="None"/>
+      </Unit>
+    </Units>
+    <JumpHistory HistoryIndex="29">
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="138" TopLine="116"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="130" Column="30" TopLine="116"/>
+      </Position>
+      <Position>
+        <Filename Value="states.pas"/>
+        <Caret Line="163" Column="11" TopLine="156"/>
+      </Position>
+      <Position>
+        <Filename Value="states.pas"/>
+        <Caret Line="191" Column="14" TopLine="170"/>
+      </Position>
+      <Position>
+        <Filename Value="states.pas"/>
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+      <Position>
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+        <Caret Line="70" Column="11" TopLine="46"/>
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+        <Filename Value="states.pas"/>
+        <Caret Line="194" Column="7" TopLine="170"/>
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+      <Position>
+        <Filename Value="states.pas"/>
+        <Caret Line="210" Column="3" TopLine="184"/>
+      </Position>
+      <Position>
+        <Filename Value="states.pas"/>
+        <Caret Line="201" Column="25" TopLine="188"/>
+      </Position>
+      <Position>
+        <Filename Value="states.pas"/>
+        <Caret Line="37" Column="22" TopLine="23"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="114" Column="11" TopLine="107"/>
+      </Position>
+      <Position>
+        <Filename Value="assets/1.slv"/>
+        <Caret Line="3" Column="12"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="42" Column="17" TopLine="35"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="55" Column="24" TopLine="35"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="68" Column="17" TopLine="59"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="13" Column="17"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="53" Column="76" TopLine="40"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="14" Column="20"/>
+      </Position>
+      <Position>
+        <Filename Value="problems.pas"/>
+        <Caret Line="90" Column="42" TopLine="74"/>
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+        <Filename Value="problems.pas"/>
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+        <Caret Line="53" Column="21" TopLine="30"/>
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+        <Caret Line="13" Column="45"/>
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+        <Filename Value="problems.pas"/>
+        <Caret Line="56" Column="35" TopLine="29"/>
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+        <Caret Line="10" Column="17"/>
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+        <Filename Value="problems.pas"/>
+        <Caret Line="120" TopLine="118"/>
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+      <Position>
+        <Filename Value="assets/1.slv"/>
+        <Caret Line="9" Column="9"/>
+      </Position>
+      <Position>
+        <Filename Value="assets/1.slv"/>
+        <Caret Column="9"/>
+      </Position>
+    </JumpHistory>
+    <RunParams>
+      <FormatVersion Value="2"/>
+      <Modes ActiveMode=""/>
+    </RunParams>
+    <HistoryLists>
+      <List Name="WorkingDirectory" Type="File" Count="1"/>
+      <List Name="LaunchingApplication" Type="File" Count="1">
+        <Item1 Value="C:\WINDOWS\system32\cmd.exe /C ${TargetCmdLine}"/>
+      </List>
+      <List Name="CommandLineParameters" Count="1"/>
+    </HistoryLists>
+  </ProjectSession>
+</CONFIG>
diff --git a/Занимательное программирование/7/4_solver/states.pas b/Занимательное программирование/7/4_solver/states.pas
new file mode 100644
index 0000000..3dbcc00
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/states.pas
@@ -0,0 +1,277 @@
+unit States;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, fgl;
+
+type
+  TPosition = record
+    X, Y: Integer
+  end;
+  TPositions = array of TPosition;
+
+  TState = class
+  private
+    PAgent: TPosition;
+    PWalls, PPlaces, PBoulders: TPositions;
+
+    procedure CopyArrays(AState: TState);
+
+  public
+    constructor Create;
+    constructor Create(ASTate: TState; AAgent: TPosition);
+    constructor Create(ASTate: TState);
+
+    property Walls: TPositions read PWalls;
+    property Places: TPositions read PPlaces;
+    property Boulders: TPositions read PBoulders;
+    property Agent: TPosition read PAgent write PAgent;
+
+    procedure AddWall(AX, AY: Integer);
+    procedure AddPlace(AX, AY: Integer);
+    procedure AddBoulder(AX, AY: Integer);
+    procedure SetAgent(AX, AY: Integer);
+    function Compare(AState: TState): Boolean;
+  end;
+  TStates = array of TState;
+
+  TBoard = class
+  private
+    PWidth, PHeight: Integer;
+    PInitialState: TState;
+
+  public
+    property Width: Integer read PWidth;
+    property Height: Integer read PHeight;
+    property InitialState: TState read PInitialState;
+
+    constructor Create(AWidth, AHeight: Integer; AInitialState: TState);
+    destructor Destroy; override;
+  end;
+
+  INode = interface
+    function GetTotalCost: Integer;
+  end;
+
+  TNode = class(TInterfacedObject, INode)
+  private
+    PState: TState;
+    PNode: TNode;
+    PCost, Heuristic: Integer;
+  public
+    property State: TState read PState;
+    property Node: TNode read PNode;
+    property Cost: Integer read PCost;
+
+    constructor Create(AState: TState; ANode: TNode; ACost, AHeuristic: Integer);
+    destructor Destroy;
+
+    function GetTotalCost: Integer;
+  end;
+  TNodes = array of TNode;
+
+  TNodeList = specialize TFPGList<TNode>;
+  TPriorityQueue = class
+  private
+    Nodes: TNodeList;
+
+  public
+    constructor Create;
+
+    procedure Add(ANode: TNode);
+    function Poll: TNode;
+    function IsEmpty: Boolean;
+    function Count: Integer;
+  end;
+
+  operator = (P1, P2: TPosition) B: Boolean;
+
+  function IsFree(NewPosition: TPosition; Walls: TPositions): Boolean;
+
+implementation
+
+procedure TSTate.CopyArrays(AState: TState);
+begin
+  PWalls := Copy(AState.Walls, 0, Length(ASTate.Walls));
+  PPlaces := Copy(AState.Places, 0, Length(ASTate.Places))
+end;
+
+constructor TState.Create;
+begin
+end;
+
+constructor TState.Create(ASTate: TState; AAgent: TPosition);
+begin
+  PAgent := AAgent;
+  CopyArrays(AState);
+  PBoulders := TPositions.Create
+end;
+
+constructor TState.Create(ASTate: TState);
+begin
+  PAgent := AState.Agent;
+  CopyArrays(AState);
+  PBoulders := Copy(AState.Boulders, 0, Length(AState.Boulders))
+end;
+
+procedure TState.AddWall(AX, AY: Integer);
+var
+  CurrentLength: Integer;
+begin
+  CurrentLength := Length(PWalls);
+  SetLength(PWalls, CurrentLength + 1);
+
+  PWalls[CurrentLength].X := AX;
+  PWalls[CurrentLength].Y := AY
+end;
+
+procedure TState.AddPlace(AX, AY: Integer);
+var
+  CurrentLength: Integer;
+begin
+  CurrentLength := Length(PPlaces);
+  SetLength(PPlaces, CurrentLength + 1);
+
+  PPlaces[CurrentLength].X := AX;
+  PPlaces[CurrentLength].Y := AY
+end;
+
+procedure TState.AddBoulder(AX, AY: Integer);
+var
+  CurrentLength: Integer;
+begin
+  CurrentLength := Length(PBoulders);
+  SetLength(PBoulders, CurrentLength + 1);
+
+  PBoulders[CurrentLength].X := AX;
+  PBoulders[CurrentLength].Y := AY
+end;
+
+procedure TState.SetAgent(AX, AY: Integer);
+begin
+  PAgent.X := AX;
+  PAgent.Y := AY
+end;
+
+function TState.Compare(AState: TState): Boolean;
+var
+  i: Integer;
+begin
+  Result := (Agent = AState.Agent)
+      and (Length(Walls) = Length(AState.Walls))
+      and (Length(Boulders) = Length(AState.Boulders))
+      and (Length(Places) = Length(AState.Places));
+  if not Result then
+    Exit;
+  for i := 0 to High(Walls) do
+    if Walls[i] <> AState.Walls[i] then
+    begin
+      Result := false;
+      Exit
+    end;
+  for i := 0 to High(Boulders) do
+    if Boulders[i] <> AState.Boulders[i] then
+    begin
+      Result := false;
+      Exit
+    end;
+  for i := 0 to High(Places) do
+    if Places[i] <> AState.Places[i] then
+    begin
+      Result := false;
+      Exit
+    end
+end;
+
+constructor TBoard.Create(AWidth, AHeight: Integer; AInitialState: TState);
+begin
+  PWidth := AWidth;
+  PHeight := AHeight;
+  PInitialState := AInitialState
+end;
+
+destructor TBoard.Destroy;
+begin
+  PInitialState.Destroy;
+  inherited
+end;
+
+constructor TNode.Create(AState: TState; ANode: TNode; ACost, AHeuristic: Integer);
+begin
+  PState := AState;
+  PNode := ANode;
+  PCost := ACost;
+  Heuristic := AHeuristic
+end;
+
+destructor TNode.Destroy;
+begin
+  PState.Free;
+  inherited
+end;
+
+function TNode.GetTotalCost: Integer;
+begin
+  Result := Cost + Heuristic
+end;
+
+constructor TPriorityQueue.Create;
+begin
+  Nodes := TNodeList.Create
+end;
+
+procedure TPriorityQueue.Add(ANode: TNode);
+var
+  Index, TotalCost: Integer;
+  CurrentNode: TNode;
+begin
+  Index := 0;
+  TotalCost := ANode.GetTotalCost;
+
+  for CurrentNode in Nodes do
+  begin
+    if CurrentNode.getTotalCost >= TotalCost then
+      break;
+    Inc(Index)
+  end;
+  Nodes.Insert(Index, ANode)
+end;
+
+function TPriorityQueue.Poll: TNode;
+begin
+  Result := Nodes.Extract(Nodes.First)
+end;
+
+function TPriorityQueue.IsEmpty: Boolean;
+begin
+  Result := Count = 0
+end;
+
+function TPriorityQueue.Count: Integer;
+begin
+  Result := Nodes.Count
+end;
+
+operator = (P1, P2: TPosition) B: Boolean;
+begin
+  B := (P1.X = P2.X) and (P1.Y = P2.Y)
+end;
+
+function IsFree(NewPosition: TPosition; Walls: TPositions): Boolean;
+var
+  Wall: TPosition;
+begin
+  for Wall in Walls do
+    if NewPosition = Wall then
+    begin
+      Result := false;
+      Exit
+    end;
+  Result := true
+end;
+
+end.
+
diff --git a/Занимательное программирование/7/4_solver/unit1.lfm b/Занимательное программирование/7/4_solver/unit1.lfm
new file mode 100644
index 0000000..2bc893a
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/unit1.lfm
@@ -0,0 +1,185 @@
+object Form1: TForm1
+  Left = 284
+  Height = 771
+  Top = 158
+  Width = 695
+  Caption = 'Form1'
+  ClientHeight = 771
+  ClientWidth = 695
+  DesignTimePPI = 120
+  LCLVersion = '4.6.0.0'
+  OnCreate = FormCreate
+  OnDestroy = FormDestroy
+  object OpenLevel: TButton
+    AnchorSideLeft.Control = Owner
+    AnchorSideLeft.Side = asrCenter
+    AnchorSideTop.Control = Owner
+    AnchorSideRight.Control = Owner
+    AnchorSideRight.Side = asrCenter
+    Left = 259
+    Height = 40
+    Top = 25
+    Width = 176
+    BorderSpacing.Top = 25
+    Caption = 'Открыть уровень'
+    TabOrder = 0
+    OnClick = OpenLevelClick
+  end
+  object BackBuffer: TImage
+    AnchorSideLeft.Control = Screen
+    AnchorSideTop.Control = Screen
+    AnchorSideRight.Control = Screen
+    AnchorSideRight.Side = asrBottom
+    AnchorSideBottom.Control = Screen
+    AnchorSideBottom.Side = asrBottom
+    Left = 25
+    Height = 384
+    Top = 90
+    Width = 640
+    Anchors = [akTop, akLeft, akRight, akBottom]
+    Visible = False
+  end
+  object Screen: TImage
+    AnchorSideLeft.Control = Owner
+    AnchorSideTop.Control = OpenLevel
+    AnchorSideTop.Side = asrBottom
+    AnchorSideRight.Control = Owner
+    AnchorSideRight.Side = asrBottom
+    AnchorSideBottom.Control = Owner
+    AnchorSideBottom.Side = asrBottom
+    Left = 25
+    Height = 384
+    Top = 90
+    Width = 640
+    BorderSpacing.Left = 25
+    BorderSpacing.Top = 25
+  end
+  object MoveList: TListBox
+    AnchorSideLeft.Control = Owner
+    AnchorSideTop.Control = Screen
+    AnchorSideTop.Side = asrBottom
+    AnchorSideRight.Control = Screen
+    AnchorSideRight.Side = asrBottom
+    AnchorSideBottom.Control = Owner
+    AnchorSideBottom.Side = asrBottom
+    Left = 25
+    Height = 247
+    Top = 499
+    Width = 640
+    Anchors = [akTop, akLeft, akRight, akBottom]
+    BorderSpacing.Left = 25
+    BorderSpacing.Top = 25
+    BorderSpacing.Bottom = 25
+    ItemHeight = 0
+    TabOrder = 1
+  end
+  object OpenDialog: TOpenDialog
+    Left = 40
+    Top = 8
+  end
+  object ImageList: TImageList
+    Height = 32
+    Width = 32
+    Left = 552
+    Top = 16
+    Bitmap = {
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+      CE20ACC4DD08DBF631180C4604FE071237534E
+    }
+  end
+end
diff --git a/Занимательное программирование/7/4_solver/unit1.pas b/Занимательное программирование/7/4_solver/unit1.pas
new file mode 100644
index 0000000..af58196
--- /dev/null
+++ b/Занимательное программирование/7/4_solver/unit1.pas
@@ -0,0 +1,177 @@
+unit Unit1;
+
+{$mode objfpc}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, ExtCtrls,
+  States, Problems;
+
+const
+  CELL_SIZE = 32;
+
+type
+
+  { TForm1 }
+
+  TForm1 = class(TForm)
+    BackBuffer: TImage;
+    ImageList: TImageList;
+    MoveList: TListBox;
+    Screen: TImage;
+    OpenLevel: TButton;
+    OpenDialog: TOpenDialog;
+    procedure FormCreate(Sender: TObject);
+    procedure FormDestroy(Sender: TObject);
+    procedure OpenLevelClick(Sender: TObject);
+  private
+
+  public
+
+  end;
+
+var
+  Form1: TForm1;
+  Board: TBoard; { Игровое поле. }
+
+implementation
+
+{$R *.lfm}
+
+{ Загрузить уровень из файла. }
+procedure LoadLevel(FileName: String);
+var
+  f: File of Char;
+  i, j, ColumnCount, CurrentColumn: Integer;
+  c: Char;
+  InitialState: TState;
+begin
+  AssignFile(f, FileName); { Открыть файл. }
+  Reset(f);
+
+  FreeAndNil(Board);
+  InitialState := TState.Create;
+
+  { Читаем первую строку, чтобы найти количество столбцов. }
+  ColumnCount := 0;
+  repeat
+    Read(f, c);
+    if c = 'x' then
+      InitialState.AddWall(ColumnCount, 0);
+    Inc(ColumnCount)
+  until c <> 'x';
+  Dec(ColumnCount);
+  Read(f, c); { Считываем и пропускаем перевод строки. }
+  j := 1;
+
+  repeat { Цикл по строкам. }
+    CurrentColumn := 0;
+
+    for i := 0 to ColumnCount - 1 do { Цикл по элементам строки. }
+    begin
+      Read(f, c); { Считаем текущий эелемент }
+
+      case c of
+        'x':
+        begin
+          InitialState.AddWall(i, j);
+          Inc(CurrentColumn)
+        end;
+        's':
+          InitialState.SetAgent(i, j);
+        'p': { Если это "место". }
+          InitialState.AddPlace(i, j);
+        'b': { Если это "камень". }
+          InitialState.AddBoulder(i, j)
+      end
+    end;
+    Inc(j);
+    Read(f, c); { считываем и пропускаем возврат каретки }
+    Read(f, c) { Считываем и пропускаем перевод строки. }
+  until CurrentColumn = ColumnCount;
+
+  Board := TBoard.Create(ColumnCount, j, InitialState);
+
+  CloseFile(f) { закрыть файл }
+end;
+
+procedure DrawCell(APosition: TPosition; Bitmap: TBitmap);
+begin
+  Form1.BackBuffer.Canvas.Draw(APosition.X * CELL_SIZE,
+      APosition.Y * CELL_SIZE,
+      Bitmap)
+end;
+
+procedure RedrawField;
+var
+  Bitmap: TBitmap;
+  ScreenRect: TRect;
+  CurrentPosition: TPosition;
+begin
+  Bitmap := TBitmap.Create; { Объект для временного хранения рисунка. }
+
+  Form1.BackBuffer.Canvas.Brush.Color := clBlack;
+  Form1.BackBuffer.Canvas.Clear;
+
+  { Рисуем стены. }
+  Form1.ImageList.GetBitmap(8, bitmap);
+  for CurrentPosition in Board.InitialState.Walls do
+    DrawCell(CurrentPosition, bitmap);
+  { Рисуем агента. }
+  Form1.ImageList.GetBitmap(4, bitmap);
+  DrawCell(Board.InitialState.Agent, Bitmap);
+
+  { Рисуем камни. }
+  Form1.ImageList.GetBitmap(2, bitmap);
+  for CurrentPosition in Board.InitialState.Boulders do
+    DrawCell(CurrentPosition, bitmap);
+
+  { Рисуем объекты. }
+  Form1.ImageList.GetBitmap(1, bitmap);
+  For CurrentPosition in Board.InitialState.Places do
+    DrawCell(CurrentPosition, bitmap);
+
+  Bitmap.Free;
+
+  { Копируем содержимое виртуального экрана на основной. }
+  ScreenRect := Rect(0, 0, Screen.Width, Screen.Height);
+  Form1.Screen.Canvas.CopyRect(ScreenRect, Form1.BackBuffer.Canvas, ScreenRect)
+end;
+
+{ TForm1 }
+
+procedure TForm1.OpenLevelClick(Sender: TObject);
+var
+  i: Integer;
+  Solution: TStates;
+  SolutionLine: String;
+begin
+  if OpenDialog.Execute then
+  begin
+    LoadLevel(OpenDialog.FileName);
+    RedrawField;
+
+    Solution := Search(Board.InitialState);
+    for i := 0 to High(Solution)  do
+    begin
+      SolutionLine := 'Agent: (' + IntToStr(Solution[i].Agent.X)
+          + ', ' + IntToStr(Solution[i].Agent.Y) + ')';
+      FreeAndNil(Solution[i]);
+      MoveList.AddItem(SolutionLine, nil)
+    end
+  end;
+end;
+
+procedure TForm1.FormCreate(Sender: TObject);
+begin
+  Board := nil
+end;
+
+procedure TForm1.FormDestroy(Sender: TObject);
+begin
+  FreeAndNil(Board)
+end;
+
+end.
+
diff --git a/Занимательное программирование/README.txt b/Занимательное программирование/README.txt
index 09b4801..b30f0ee 100644
--- a/Занимательное программирование/README.txt
+++ b/Занимательное программирование/README.txt
@@ -20,5 +20,5 @@ Lazarus.
 только теоретические задания.
 
 Седьмая глава "Простые компьютерные игры" применяет Lazarus. Изображения
-для частично сделаны заново, частично скопированы из приложения книги
-и отредактированы.
+частично сделаны заново, частично скопированы из приложения книги и
+отредактированы.