day 18, part 2 (complete solution)

day18-hard/src/main.zig

@@ -119,6 +119,39 @@ fn readNumber(comptime T: type, line: []const u8, index: *usize) T {
     return if (is_negative) (0 - result) else result;
 }
 
+fn readHexNumber(comptime T: type, line: []const u8, index: *usize) T {
+    var result: T = 0;
+    while (index.* < line.len and line[index.*] == ' ') : (index.* += 1) {}
+
+    var is_negative = false;
+    if (index.* < line.len and line[index.*] == '-') {
+        is_negative = true;
+        index.* += 1;
+    }
+
+    std.debug.assert(index.* < line.len);
+
+    while (index.* < line.len) : (index.* += 1) {
+        const char = line[index.*];
+        switch (char) {
+            '0'...'9' => {
+                result = result * 16 + (char - '0');
+            },
+            'a'...'f' => {
+                result = result * 16 + 10 + (char - 'a');
+            },
+            'A'...'F' => {
+                result = result * 16 + 10 + (char - 'A');
+            },
+            else => {
+                break;
+            },
+        }
+    }
+
+    return if (is_negative) (0 - result) else result;
+}
+
 fn Coordinates(comptime CoordinateType: type) type {
     return struct {
         const Self = @This();
@@ -184,7 +217,7 @@ const CellStatus = enum(u2) {
 
 const TerrainCoordinate = u16;
 
-const Terrain = GenericTerrain(TerrainCoordinate, 1024, 1024, CellStatus);
+const Terrain = GenericTerrain(TerrainCoordinate, 2048, 2048, CellStatus);
 
 const TerrainCoordinates = Coordinates(TerrainCoordinate);
 
@@ -195,12 +228,14 @@ const Direction = enum(u8) {
     Up = 3,
 };
 
+const RawCoordinate = u32;
+
 const RawCommand = packed struct(u32) {
     direction: Direction,
     length: u24,
 };
 
-const RawCoordinates = Coordinates(u24);
+const RawCoordinates = Coordinates(RawCoordinate);
 
 fn floodTerrain(terrain: *Terrain) void {
     var queue_mem: [65_536]TerrainCoordinates = undefined;
@@ -238,7 +273,7 @@ fn floodTerrain(terrain: *Terrain) void {
 }
 
 fn getTargetRawCoordinates(coordinates: RawCoordinates, command: RawCommand) RawCoordinates {
-    return @TypeOf(coordinates){
+    return RawCoordinates{
         .x = switch (command.direction) {
             .Right => coordinates.x + command.length,
             .Left => coordinates.x - command.length,
@@ -252,8 +287,8 @@ fn getTargetRawCoordinates(coordinates: RawCoordinates, command: RawCommand) Raw
     };
 }
 
-fn getCoordinate(known_values: []const u24, raw_coordinate: u24) TerrainCoordinate {
-    const maybe_index = std.sort.binarySearch(u24, raw_coordinate, known_values, {}, Order(u24).order);
+fn getCoordinate(known_values: []const RawCoordinate, raw_coordinate: RawCoordinate) TerrainCoordinate {
+    const maybe_index = std.sort.binarySearch(RawCoordinate, raw_coordinate, known_values, {}, Order(RawCoordinate).order);
     return @as(TerrainCoordinate, @intCast(maybe_index.?));
 }
 
@@ -263,12 +298,12 @@ fn solveForCommands(raw_commands: []const RawCommand) usize {
         .x = start_value,
         .y = start_value,
     };
-    var known_values = StackList(u24, u16, 2048).init();
+    var known_values = StackList(RawCoordinate, u16, 2048).init();
     known_values.addUnique(0);
     known_values.addUnique(start_value - 1);
     known_values.addUnique(start_value);
     known_values.addUnique(start_value + 1);
-    known_values.addUnique(std.math.maxInt(u24));
+    known_values.addUnique(std.math.maxInt(RawCoordinate));
     for (raw_commands) |raw_command| {
         raw_coordinates = getTargetRawCoordinates(raw_coordinates, raw_command);
         known_values.addUnique(raw_coordinates.x - 1);
@@ -279,7 +314,7 @@ fn solveForCommands(raw_commands: []const RawCommand) usize {
         known_values.addUnique(raw_coordinates.y + 1);
     }
 
-    std.sort.heap(u24, known_values.getMutableSlice(), {}, std.sort.asc(u24));
+    std.sort.heap(RawCoordinate, known_values.getMutableSlice(), {}, std.sort.asc(RawCoordinate));
 
     var known_values_slice = known_values.getSlice();
 
@@ -331,17 +366,19 @@ fn solveForCommands(raw_commands: []const RawCommand) usize {
 
 fn parseCommand(command: []const u8) RawCommand {
     var index: usize = 2;
-    const length = readNumber(u24, command, &index);
-    const direction: Direction = switch (command[0]) {
-        'R' => .Right,
-        'L' => .Left,
-        'U' => .Up,
-        'D' => .Down,
+    _ = readNumber(u8, command, &index);
+    index += 3;
+    const value = readHexNumber(u24, command, &index);
+    const direction: Direction = switch (value % 16) {
+        0 => .Right,
+        1 => .Down,
+        2 => .Left,
+        3 => .Up,
         else => unreachable,
     };
 
     return .{
-        .length = length,
+        .length = value / 16,
         .direction = direction,
     };
 }