From 474cfa6cc37b398675613764d3318cfa38620bc6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20M=C3=BCller?= <stefan.mueller@aksdb.de>
Date: Tue, 5 Dec 2023 18:14:14 +0100
Subject: [PATCH] Updated solution for "Day 5: If You Give A Seed A
 Fertilizer", part 1, to process the data just in time instead of preloading
 all of it

---
 UGiveSeedFertilizer.pas | 125 ++++++++++++++++++++--------------------
 1 file changed, 62 insertions(+), 63 deletions(-)

diff --git a/UGiveSeedFertilizer.pas b/UGiveSeedFertilizer.pas
index dc44a6b..cc4b76a 100644
--- a/UGiveSeedFertilizer.pas
+++ b/UGiveSeedFertilizer.pas
@@ -32,29 +32,19 @@ type
   private
     FDestinationStart, FSourceStart, FSourceEnd, FDifference1, FDifference2: Cardinal;
   public
+    constructor Create(const ALine: string);
     constructor Create(const ADestinationStart, ASourceStart, ALength: Cardinal);
     function TryConvert(const AInput: Cardinal; out OOutput: Cardinal): Boolean;
   end;
 
-  { TAlmanacMap }
-
-  TAlmanacMap = class
-  private
-    FRanges: specialize TFPGObjectList<TAlmanacMapRange>;
-  public
-    constructor Create;
-    destructor Destroy; override;
-    procedure AddMapRange(const ALine: string);
-    function Convert(const AInput: Cardinal): Cardinal;
-  end;
-
   { TGiveSeedFertilizer }
 
   TGiveSeedFertilizer = class(TSolver)
   private
-    FSeeds: specialize TFPGList<Cardinal>;
-    FMaps: specialize TFPGObjectList<TAlmanacMap>;
+    FNew, FConverted, FProcessedIndices: specialize TFPGList<Cardinal>;
     procedure ProcessSeeds(const ALine: string);
+    procedure ProcessMapRange(const ALine: string);
+    procedure FinishMap;
   public
     constructor Create;
     destructor Destroy; override;
@@ -68,6 +58,14 @@ implementation
 
 { TAlmanacMapRange }
 
+constructor TAlmanacMapRange.Create(const ALine: string);
+var
+  split: TStringArray;
+begin
+  split := ALine.Split(' ');
+  Create(StrToDWord(split[0]), StrToDWord(split[1]), StrToDWord(split[2]));
+end;
+
 constructor TAlmanacMapRange.Create(const ADestinationStart, ASourceStart, ALength: Cardinal);
 begin
   FDestinationStart := ADestinationStart;
@@ -106,40 +104,6 @@ begin
   end;
 end;
 
-{ TAlmanacMap }
-
-constructor TAlmanacMap.Create;
-begin
-  FRanges := specialize TFPGObjectList<TAlmanacMapRange>.Create;
-end;
-
-destructor TAlmanacMap.Destroy;
-begin
-  FRanges.Free;
-  inherited Destroy;
-end;
-
-procedure TAlmanacMap.AddMapRange(const ALine: string);
-var
-  split: TStringArray;
-begin
-  split := ALine.Split(' ');
-  FRanges.Add(TAlmanacMapRange.Create(StrToDWord(split[0]), StrToDWord(split[1]), StrToDWord(split[2])));
-end;
-
-function TAlmanacMap.Convert(const AInput: Cardinal): Cardinal;
-var
-  range: TAlmanacMapRange;
-begin
-  for range in FRanges do
-  begin
-    if range.TryConvert(AInput, Result) then
-      Exit;
-  end;
-
-  Result := AInput;
-end;
-
 { TGiveSeedFertilizer }
 
 procedure TGiveSeedFertilizer.ProcessSeeds(const ALine: string);
@@ -150,20 +114,60 @@ begin
   split := Aline.Split(' ');
   for i := 1 to Length(split) - 1 do
   begin
-    FSeeds.Add(StrToDWord(split[i]));
+    FNew.Add(StrToDWord(split[i]));
   end;
 end;
 
+procedure TGiveSeedFertilizer.ProcessMapRange(const ALine: string);
+var
+  range: TAlmanacMapRange;
+  i: Integer;
+  converted: Cardinal;
+begin
+  // Converts all "new" values that fall into this mapping range.
+  range := TAlmanacMapRange.Create(ALine);
+  for i := 0 to FNew.Count - 1 do
+  begin
+    if range.TryConvert(FNew[i], converted) then
+    begin
+      FConverted.Add(converted);
+      FProcessedIndices.Add(i);
+    end;
+  end;
+  range.Free;
+
+  // Forgets the converted values.
+  for i := FProcessedIndices.Count - 1 downto 0 do
+  begin
+    FNew.Delete(FProcessedIndices[i]);
+  end;
+  FProcessedIndices.Clear;
+end;
+
+procedure TGiveSeedFertilizer.FinishMap;
+var
+  value: Cardinal;
+begin
+  // Resets the lists for the next map, remaining values stay unconverted.
+  for value in FConverted do
+  begin
+    FNew.Add(value);
+  end;
+  FConverted.Clear;
+end;
+
 constructor TGiveSeedFertilizer.Create;
 begin
-  FSeeds := specialize TFPGList<Cardinal>.Create;
-  FMaps := specialize TFPGObjectList<TAlmanacMap>.Create;
+  FNew := specialize TFPGList<Cardinal>.Create;
+  FConverted := specialize TFPGList<Cardinal>.Create;
+  FProcessedIndices := specialize TFPGList<Cardinal>.Create;
 end;
 
 destructor TGiveSeedFertilizer.Destroy;
 begin
-  FSeeds.Free;
-  FMaps.Free;
+  FNew.Free;
+  FConverted.Free;
+  FProcessedIndices.Free;
   inherited Destroy;
 end;
 
@@ -172,23 +176,18 @@ begin
   if LeftStr(ALine, 6) = 'seeds:' then
     ProcessSeeds(ALine)
   else if RightStr(ALine, 4) = 'map:' then
-    FMaps.Add(TAlmanacMap.Create)
+    FinishMap
   else if Aline <> '' then
-    FMaps.Last.AddMapRange(ALine);
+    ProcessMapRange(ALine);
 end;
 
 procedure TGiveSeedFertilizer.Finish;
 var
-  seed, value: Cardinal;
-  map: TAlmanacMap;
+  value: Cardinal;
 begin
-  for seed in FSeeds do
+  FinishMap;
+  for value in FNew do
   begin
-    value := seed;
-    for map in FMaps do
-    begin
-      value := map.Convert(value);
-    end;
     if (FPart1 = 0) or (value < FPart1) then
       FPart1 := value;
   end;