day 18, part 1 (improved in preparation to part 2)

day18-easy/src/main.zig

@@ -1,5 +1,49 @@
 const std = @import("std");
 
+fn StackList(comptime T: type, comptime capacity_type: type, comptime capacity: capacity_type) type {
+    return struct {
+        const Self = @This();
+        mem: [capacity]T,
+        length: capacity_type,
+
+        fn add(self: *Self, value: T) void {
+            self.mem[self.length] = value;
+            self.length += 1;
+        }
+
+        fn addIfNotNull(self: *Self, nullable_value: ?T) void {
+            if (nullable_value) |value| {
+                self.add(value);
+            }
+        }
+
+        fn has(self: *Self, needle: T) bool {
+            for (0..self.length) |i| {
+                if (self.mem[i] == needle) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        fn getMutableSlice(self: *Self) []T {
+            return (&self.mem)[0..self.length];
+        }
+
+        fn getSlice(self: *const Self) []const T {
+            return self.mem[0..self.length];
+        }
+
+        fn init() Self {
+            return Self{
+                .mem = undefined,
+                .length = 0,
+            };
+        }
+    };
+}
+
 fn RingQueueWrapper(comptime T: type, comptime size: usize) type {
     return struct {
         const Self = @This();
@@ -87,6 +131,18 @@ const FloodTask = struct {
     y: TerrainCoordinate,
 };
 
+const Direction = enum(u8) {
+    Right = 0,
+    Down = 1,
+    Left = 2,
+    Up = 3,
+};
+
+const Command = packed struct(u32) {
+    direction: Direction,
+    length: u24,
+};
+
 fn floodTerrain(terrain: *Terrain) void {
     var queue_mem: [65_536]FloodTask = undefined;
     var tasks = RingQueueWrapper(FloodTask, queue_mem.len).init(&queue_mem);
@@ -138,34 +194,71 @@ fn solveForTerrain(terrain: *Terrain) usize {
     return result;
 }
 
-fn dig(terrain: *Terrain, command: []const u8) void {
-    var index: usize = 2;
-    const length = readNumber(usize, command, &index);
-    const direction = command[0];
-
-    for (0..length) |i| {
-        _ = i;
-        terrain.*.x = switch (direction) {
-            'R' => terrain.*.x + 1,
-            'L' => terrain.*.x - 1,
-            else => terrain.*.x,
-        };
-
-        terrain.*.y = switch (direction) {
-            'D' => terrain.*.y + 1,
-            'U' => terrain.*.y - 1,
-            else => terrain.*.y,
-        };
-
-        //std.debug.print("digging {d},{d}\n", .{ terrain.*.x, terrain.*.y });
+fn dig(terrain: *Terrain, command: Command) void {
+    const target_x = switch (command.direction) {
+        .Right => terrain.*.x + command.length,
+        .Left => terrain.*.x - command.length,
+        .Up, .Down => terrain.*.x,
+    };
+
+    const target_y = switch (command.direction) {
+        .Down => terrain.*.y + command.length,
+        .Up => terrain.*.y - command.length,
+        .Left, .Right => terrain.*.y,
+    };
+
+    while (terrain.*.x != target_x) {
+        if (terrain.*.x < target_x) {
+            terrain.*.x += 1;
+        } else {
+            terrain.*.x -= 1;
+        }
+
         terrain.*.cells[terrain.*.x][terrain.*.y] = .Dug;
     }
+
+    while (terrain.*.y != target_y) {
+        if (terrain.*.y < target_y) {
+            terrain.*.y += 1;
+        } else {
+            terrain.*.y -= 1;
+        }
+
+        terrain.*.cells[terrain.*.x][terrain.*.y] = .Dug;
+    }
+}
+
+fn parseCommand(command: []const u8) Command {
+    var index: usize = 2;
+    const length = readNumber(u24, command, &index);
+    const direction: Direction = switch (command[0]) {
+        'R' => .Right,
+        'L' => .Left,
+        'U' => .Up,
+        'D' => .Down,
+        else => unreachable,
+    };
+
+    return .{
+        .length = length,
+        .direction = direction,
+    };
+}
+
+fn solveForCommands(commands: []const Command) usize {
+    var terrain = Terrain.initZeroes();
+
+    for (commands) |command| {
+        dig(&terrain, command);
+    }
+
+    return solveForTerrain(&terrain);
 }
 
 fn solveAll(reader: anytype) !usize {
     var result: usize = 0;
     while (true) {
-        var terrain = Terrain.initZeroes();
+        var commands = StackList(Command, usize, 1024).init();
 
         var empty_line_reached = false;
         var line_buffer: [1000]u8 = undefined;
@@ -174,10 +267,10 @@ fn solveAll(reader: anytype) !usize {
                 empty_line_reached = true;
                 break;
             }
-            dig(&terrain, line);
+            commands.add(parseCommand(line));
         }
 
-        result += solveForTerrain(&terrain);
+        result += solveForCommands(commands.getSlice());
 
         if (!empty_line_reached) {
             return result;