Solution for day 17.

Author: thorstel

.gitignore

@@ -1,2 +1,3 @@
 *.exe
 obj
+*.out

day17/day17.adb

@@ -0,0 +1,123 @@
+with Ada.Text_IO; use Ada.Text_IO;
+with Input17;     use Input17;
+
+procedure Day17 is
+
+   Grid : array
+     (Natural range 0 .. 2000, Natural range 0 .. 2000) of Character :=
+     (others => (others => '.'));
+
+   Min_X, Min_Y : Natural := Natural'Last;
+   Max_X, Max_Y : Natural := Natural'First;
+
+   function Can_Spread (X, Y : Natural) return Boolean is
+     (Grid (X, Y) = '.' or Grid (X, Y) = '|');
+
+   procedure Spread_Water (X, Y : Natural) is
+   begin
+      if Y > Max_Y then
+         return;
+      end if;
+      if not Can_Spread (X, Y) then
+         return;
+      end if;
+      if not Can_Spread (X, Y + 1) then
+         declare
+            Left_X  : Natural := X;
+            Right_X : Natural := X + 1;
+         begin
+            while Can_Spread (Left_X, Y) and not Can_Spread (Left_X, Y + 1)
+            loop
+               Grid (Left_X, Y) := '|';
+               Left_X           := Left_X - 1;
+            end loop;
+            while Can_Spread (Right_X, Y) and not Can_Spread (Right_X, Y + 1)
+            loop
+               Grid (Right_X, Y) := '|';
+               Right_X           := Right_X + 1;
+            end loop;
+            if Can_Spread (Left_X, Y + 1) or Can_Spread (Right_X, Y + 1) then
+               Spread_Water (Left_X, Y);
+               Spread_Water (Right_X, Y);
+            elsif Grid (Left_X, Y) = '#' and Grid (Right_X, Y) = '#' then
+               for X2 in Left_X + 1 .. Right_X - 1 loop
+                  Grid (X2, Y) := '~';
+               end loop;
+            end if;
+         end;
+      elsif Grid (X, Y) = '.' then
+         Grid (X, Y) := '|';
+         Spread_Water (X, Y + 1);
+         if Grid (X, Y + 1) = '~' then
+            Spread_Water (X, Y);
+         end if;
+      end if;
+   end Spread_Water;
+
+begin
+   for I in X_Inputs'Range loop
+      Min_X := Natural'Min (Min_X, X_Inputs (I).Fixed);
+      Max_X := Natural'Max (Max_X, X_Inputs (I).Fixed);
+      Min_Y := Natural'Min (Min_Y, X_Inputs (I).First);
+      Max_Y := Natural'Max (Max_Y, X_Inputs (I).Last);
+   end loop;
+   for I in Y_Inputs'Range loop
+      Min_Y := Natural'Min (Min_Y, Y_Inputs (I).Fixed);
+      Max_Y := Natural'Max (Max_Y, Y_Inputs (I).Fixed);
+      Min_X := Natural'Min (Min_X, Y_Inputs (I).First);
+      Max_X := Natural'Max (Max_X, Y_Inputs (I).Last);
+   end loop;
+
+   for I in X_Inputs'Range loop
+      declare
+         X : constant Natural := X_Inputs (I).Fixed;
+      begin
+         for Y in X_Inputs (I).First .. X_Inputs (I).Last loop
+            Grid (X, Y) := '#';
+         end loop;
+      end;
+   end loop;
+   for I in Y_Inputs'Range loop
+      declare
+         Y : constant Natural := Y_Inputs (I).Fixed;
+      begin
+         for X in Y_Inputs (I).First .. Y_Inputs (I).Last loop
+            Grid (X, Y) := '#';
+         end loop;
+      end;
+   end loop;
+
+   Spread_Water (500, Min_Y);
+
+   declare
+      Water_Tiles : Natural := 0;
+      Perma_Water : Natural := 0;
+   begin
+      for Y in Min_Y .. Max_Y loop
+         for X in 0 .. 2000 loop
+            if Grid (X, Y) = '~' then
+               Perma_Water := Perma_Water + 1;
+               Water_Tiles := Water_Tiles + 1;
+            elsif Grid (X, Y) = '|' then
+               Water_Tiles := Water_Tiles + 1;
+            end if;
+         end loop;
+      end loop;
+      Put_Line ("Part 1 =" & Natural'Image (Water_Tiles));
+      Put_Line ("Part 2 =" & Natural'Image (Perma_Water));
+   end;
+
+   -- Write the whole grid to a file (just for fun).
+   declare
+      File : File_Type;
+   begin
+      Create (File, Out_File, "grid.out");
+      for Y in Min_Y .. Max_Y loop
+         for X in Min_X .. Max_X loop
+            Put (File, Grid (X, Y));
+         end loop;
+         Put_Line (File, "");
+      end loop;
+      Close (File);
+   end;
+end Day17;

day17/day17.gpr

@@ -0,0 +1,8 @@
+project day17 is
+    for Object_Dir use "obj";
+    for Main use ("day17.adb");
+    for Exec_Dir use ".";
+    package Compiler is
+       for Switches ("Ada") use ("-Wall", "-g", "-O2");
+    end Compiler;
+end day17;