94 lines
2.1 KiB
Plaintext
94 lines
2.1 KiB
Plaintext
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{
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Solutions to the Advent Of Code.
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Copyright (C) 2024 Stefan Müller
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This program is free software: you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free Software
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Foundation, either version 3 of the License, or (at your option) any later
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version.
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This program is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along with
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this program. If not, see <http://www.gnu.org/licenses/>.
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}
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unit UBinomialCoefficients;
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{$mode ObjFPC}{$H+}
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interface
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uses
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Classes, SysUtils, Generics.Collections;
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type
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TCardinalArray = array of Cardinal;
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TCardinalArrays = specialize TList<TCardinalArray>;
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{ TBinomialCoefficientCache }
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TBinomialCoefficientCache = class
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private
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FCache: TCardinalArrays;
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procedure AddRow;
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public
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constructor Create;
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destructor Destroy; override;
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function Get(const AN, AK: Cardinal): Cardinal;
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function GetCachedRowsCount: Cardinal;
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end;
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implementation
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{ TBinomialCoefficientCache }
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procedure TBinomialCoefficientCache.AddRow;
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var
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row: TCardinalArray;
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i: Cardinal;
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begin
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SetLength(row, FCache.Count + 1);
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row[0] := 1;
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if FCache.Count > 0 then
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begin
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row[FCache.Count] := 1;
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for i := 1 to FCache.Count - 1 do
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row[i] := FCache.Last[i - 1] + FCache.Last[i];
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end;
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FCache.Add(row);
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end;
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constructor TBinomialCoefficientCache.Create;
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begin
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FCache := TCardinalArrays.Create;
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end;
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destructor TBinomialCoefficientCache.Destroy;
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begin
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FCache.Free;
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inherited Destroy;
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end;
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function TBinomialCoefficientCache.Get(const AN, AK: Cardinal): Cardinal;
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var
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i: Cardinal;
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begin
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if AN < AK then
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raise ERangeError.Create('Cannot calculate binomial coefficient "n choose k" with k larger than n.');
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for i := FCache.Count to AN do
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AddRow;
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Result := FCache[AN][AK];
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end;
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function TBinomialCoefficientCache.GetCachedRowsCount: Cardinal;
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begin
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Result := FCache.Count;
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end;
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end.
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