• Delphi中的THashTable


    在Delphi中,Inifiles单元中有一个TStringHash的类,不过它的Value仅支持Integer(其实也不是问题,有其它类型可以将变量变为Pointer),有点不舒服,今天没事做就把它替换为variant了,其中Key的名称大小写无关,就是为了加快开发速度!

    使用Hashtable,查找和删除复杂度都是常数级别的!

    type
      PPHashItem = ^PHashItem;
      PHashItem = ^THashItem;
      THashItem = record
        Next: PHashItem;
        Key: String;
        Value: Variant;
      end;
      THashTable = class
      private
        Buckets: array of PHashItem;
      protected
        function Find(const Key: String): PPHashItem;
        function HashOf(const Key: String): Cardinal; virtual;
      public
        constructor Create(Size: Cardinal = 256);
        destructor Destroy; override;
        procedure Put(const Key: String; Value: Variant);
        procedure Clear;
        procedure Remove(const Key: String);
        function Modify(const Key: String; Value: Variant): Boolean;
        function Get(const Key: String): Variant;
        function ContainKey(const Key: String):boolean;
      end;
    procedure THashTable.Clear;
    var
      I: Integer;
      P, N: PHashItem;
    begin
      for I := 0 to Length(Buckets) - 1 do
      begin
        P := Buckets[I];
        while P <> nil do
        begin
          N := P^.Next;
          Dispose(P);
          P := N;
        end;
        Buckets[I] := nil;
      end;
    end;
    function THashTable.ContainKey(const Key: String): boolean;
    var
      P: PHashItem;
    begin
      P := Find(Key)^;
      if P <> nil then
      begin
        Result := True;
      end
      else
        Result := False;
    end;
    constructor THashTable.Create(Size: Cardinal);
    begin
      inherited Create;
      SetLength(Buckets, Size);
    end;
    destructor THashTable.Destroy;
    begin
      Clear;
      inherited Destroy;
    end;
    function THashTable.Find(const Key: String): PPHashItem;
    var
      Hash: Integer;
    begin
      Hash := HashOf(Key) mod Cardinal(Length(Buckets));
      Result := @Buckets[Hash];
      while Result^ <> nil do
      begin
        if Result^.Key = Key then
          Exit
        else
          Result := @Result^.Next;
      end;
    end;
    function THashTable.Get(const Key: String): Variant;
    var
      P: PHashItem;
    begin
      P := Find(AnsiUpperCase(Key))^;
      if P <> nil then
        Result := P^.Value
      else
        Result := -1;
    end;
    function THashTable.HashOf(const Key: String): Cardinal;
    var
      I: Integer;
    begin
      Result := 0;
      for I := 1 to Length(Key) do
        Result := ((Result shl 2) or (Result shr (SizeOf(Result) * 8 - 2))) xor
          Ord(Key[I]);
    end;
    function THashTable.Modify(const Key: String; Value: Variant): Boolean;
    var
      P: PHashItem;
    begin
      P := Find(Key)^;
      if P <> nil then
      begin
        Result := True;
        P^.Value := Value;
      end
      else
        Result := False;
    end;
    procedure THashTable.Put(const Key: String; Value: Variant);
    var
      Hash: Integer;
      Bucket: PHashItem;
    begin
      Hash := HashOf(AnsiUpperCase(Key)) mod Cardinal(Length(Buckets));
      New(Bucket);
      Bucket^.Key := AnsiUpperCase(Key);
      Bucket^.Value := Value;
      Bucket^.Next := Buckets[Hash];
      Buckets[Hash] := Bucket;
    end;
    procedure THashTable.Remove(const Key: String);
    var
      P: PHashItem;
      Prev: PPHashItem;
    begin
      Prev := Find(Key);
      P := Prev^;
      if P <> nil then
      begin
        Prev^ := P^.Next;
        Dispose(P);
      end;
    end;
    View Code
    使用
    
    
    
    
    
    
    
    
    
    
    
    
    var
      Demo:THashTable;
    begin
      Demo:=THashTable.Create();
      try
        Demo.Put('id',1);
        ShowMessage(Demo.Get('id'));
      finally
        Demo.Free;
      end;
    end;
    View Code
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  • 原文地址:https://www.cnblogs.com/key-ok/p/3358929.html
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