Added solution for "Day 9: Mirage Maintenance", part 2

solvers/UMirageMaintenance.pas

@@ -31,7 +31,7 @@ type
   TMirageMaintenance = class(TSolver)
   private
     FN: Integer;
-    FLagrangePolynomialsInN: specialize TList<Int64>;
+    FLagrangePolynomialsInN, FLagrangePolynomialsInMinusOne: specialize TList<Int64>;
     procedure CalcLagrangePolynomials;
   public
     constructor Create;
@@ -48,19 +48,23 @@ implementation
 
 procedure TMirageMaintenance.CalcLagrangePolynomials;
 var
-  sign, i, j: Integer;
+  sign1, sign2, i, j: Integer;
 begin
   FLagrangePolynomialsInN.Clear;
+  FLagrangePolynomialsInMinusOne.Clear;
   if FN mod 2 = 0 then
-    sign := -1
+    sign1 := -1
   else
-    sign := 1;
+    sign1 := 1;
+  sign2 := 1;
 
   // Calculates the polynomials in N and -1.
   for i := 0 to FN - 1 do
   begin
-    FLagrangePolynomialsInN.Add(sign);
+    FLagrangePolynomialsInN.Add(sign1);
-    sign := -sign;
+    sign1 := -sign1;
+    FLagrangePolynomialsInMinusOne.Add(sign2);
+    sign2 := -sign2;
 
     if i < FN - FN div 2 then
     begin
@@ -81,18 +85,38 @@ begin
       for j := 2 to FN - i - 1 do
         FLagrangePolynomialsInN[i] := FLagrangePolynomialsInN[i] div j;
     end;
-  end;
+
+    if i < FN div 2 then
+    begin
+      // Multiplies by the non-cancelled numerator terms.
+      for j := FN - i to FN do
+        FLagrangePolynomialsInMinusOne[i] := FLagrangePolynomialsInMinusOne[i] * j;
+      // Divides by the non-cancelled denominator terms.
+      for j := 2 to i + 1 do
+        FLagrangePolynomialsInMinusOne[i] := FLagrangePolynomialsInMinusOne[i] div j;
+    end
+    else begin
+      // Multiplies by the non-cancelled numerator terms.
+      for j := i + 2 to FN do
+        FLagrangePolynomialsInMinusOne[i] := FLagrangePolynomialsInMinusOne[i] * j;
+      // Divides by the non-cancelled denominator terms.
+      for j := 2 to FN - i - 1 do
+        FLagrangePolynomialsInMinusOne[i] := FLagrangePolynomialsInMinusOne[i] div j;
+    end;
+end;
 end;
 
 constructor TMirageMaintenance.Create;
 begin
   FLagrangePolynomialsInN := specialize TList<Int64>.Create;
+  FLagrangePolynomialsInMinusOne := specialize TList<Int64>.Create;
   FN := 0;
 end;
 
 destructor TMirageMaintenance.Destroy;
 begin
   FLagrangePolynomialsInN.Free;
+  FLagrangePolynomialsInMinusOne.Free;
   inherited Destroy;
 end;
 
@@ -114,6 +138,8 @@ begin
     y := StrToInt(split[i]);
     p := y * FLagrangePolynomialsInN[i];
     Inc(FPart1, p);
+    p := y * FLagrangePolynomialsInMinusOne[i];
+    Inc(FPart2, p);
   end;
 end;
 

tests/UMirageMaintenanceTestCases.pas

@@ -62,7 +62,7 @@ end;
 
 procedure TMirageMaintenanceFullDataTestCase.TestPart2;
 begin
-  AssertEquals(-1, FSolver.GetResultPart2);
+  AssertEquals(1108, FSolver.GetResultPart2);
 end;
 
 { TMirageMaintenanceExampleTestCase }
@@ -79,7 +79,7 @@ end;
 
 procedure TMirageMaintenanceExampleTestCase.TestPart2;
 begin
-  AssertEquals(-1, FSolver.GetResultPart2);
+  AssertEquals(2, FSolver.GetResultPart2);
 end;
 
 initialization