day 21, part 1

day21-easy/build.zig

@@ -0,0 +1,70 @@
+const std = @import("std");
+
+// Although this function looks imperative, note that its job is to
+// declaratively construct a build graph that will be executed by an external
+// runner.
+pub fn build(b: *std.Build) void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    // Standard optimization options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
+    // set a preferred release mode, allowing the user to decide how to optimize.
+    const optimize = b.standardOptimizeOption(.{});
+
+    const exe = b.addExecutable(.{
+        .name = "day21-easy",
+        // In this case the main source file is merely a path, however, in more
+        // complicated build scripts, this could be a generated file.
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    // This declares intent for the executable to be installed into the
+    // standard location when the user invokes the "install" step (the default
+    // step when running `zig build`).
+    b.installArtifact(exe);
+
+    // This *creates* a Run step in the build graph, to be executed when another
+    // step is evaluated that depends on it. The next line below will establish
+    // such a dependency.
+    const run_cmd = b.addRunArtifact(exe);
+
+    // By making the run step depend on the install step, it will be run from the
+    // installation directory rather than directly from within the cache directory.
+    // This is not necessary, however, if the application depends on other installed
+    // files, this ensures they will be present and in the expected location.
+    run_cmd.step.dependOn(b.getInstallStep());
+
+    // This allows the user to pass arguments to the application in the build
+    // command itself, like this: `zig build run -- arg1 arg2 etc`
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // and can be selected like this: `zig build run`
+    // This will evaluate the `run` step rather than the default, which is "install".
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+
+    // Creates a step for unit testing. This only builds the test executable
+    // but does not run it.
+    const unit_tests = b.addTest(.{
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    const run_unit_tests = b.addRunArtifact(unit_tests);
+
+    // Similar to creating the run step earlier, this exposes a `test` step to
+    // the `zig build --help` menu, providing a way for the user to request
+    // running the unit tests.
+    const test_step = b.step("test", "Run unit tests");
+    test_step.dependOn(&run_unit_tests.step);
+}

day21-easy/easy.in

@@ -0,0 +1,131 @@
+...................................................................................................................................
+..............#...#........#...............#.#.......#....##...........#.#..#......#.....#.........#..##...........................
+.#..##..##..#......#.#.#...##......###...##......#.#..#...................#.....#..........#..#................#...#..........#....
+.....................#..#.......#.....##.........#.......................................#........#....#.#..........#.#......#.#...
+......##...#.....#.......#...#..###..........#..........#......................#........#.............#.....#........#....#........
+.................##.................#...#.........#................................#........#...........#............#........#....
+..............#.#....#........##.....##..........#.............##.............#...#......#..##..........#.........#.....#...#..#...
+..#....#.......#...##..#......#.........#.#..#....#.#..............#........#...#...#...............#.#.....#..#..##......#...#....
+...#......##...##..#...#..........#...#..........#..............#...#..........#..#..#..#........#.#.#.#.#...........###...........
+.#.#.#...#.#...##............................................#......................#...#......#......##.#.........................
+.##.#.........#...#..................##...........#............#..................###...#...........#.................#....#.......
+.....................#...#.#................#................#.#........................#...#...##....##....#.#...#.........#...#..
+...#.......#...#.........................#.#..................#........##..........................#......##....##............#....
+......................#.....................#...............#.......#.#...................#...............#...#........#.##......#.
+............................#..........................#........#....#.##..#.......#.##..#...#.#..#...............#.#..#....#......
+.......................................................#.#..#.#....#......................#............#....#..#.......#.........#.
+.....##........#...............#.......#...............#.#..........##..#...................#................#..#...#.#....#...###.
+....#.....................##................#.......#.......#...#.#...#...............#................#...............##..........
+....#........#..#.......#.#.#........................#.#...........#.......#..#.........#....#.......#........#.#.#................
+......###.....#..#...........#.....#..#..#........#......#.#........###.....##............#..#...........#.........................
+.....#...........#...................#..#..........#..#...###.#.........#.##...............#..##..........#.........#..............
+.#.........#....#............#.##..........................##.....#........#....#.............#.......#...#..............##.#......
+.#..#...#.......#...#.......##.......#.#.............................#...#...#.#...........#...#.................#.........#.#.#...
+...#....................#.....##..............#.................#.................#............#......#....#.......#.........#.....
+.......#...#.............#.##...#.#...................#.....#..#........#................................#.............#..#...##...
+...#.###..............#....#........................#......#...#.........#......#.#....................#........#...#...#.......#..
+............#.#...#...........................#....###.###...#........#..#........#...................##.....###......#........#...
+.....#...#................#.##..##..................#....#.........#............##...................##................#.....#.....
+.#....#..............##...#..................#......#..........##.#....#......##.#...............#....##..............#....#.......
+....#.#.##...........##.....#...........#.........#...#........#..#.......#......#................#.#...#....#...#.................
+.......#...#...#...#..#.......#..........#..................#..#........#..#.#.....#.#.....................##......................
+.....##.........#.......##...#.............#.##.#.#...#.##.#...#......#...#....#.......#..#.........#...........#.##.###.#.....#...
+...................#.#.......................#.....#.#......#.....##...#.#....#..#..........#...........#..##....#...#.......#.#...
+.....#..#..#.........#...#.#.........#...#.#...##...#......##........#...............#.......#................#.....#...#.#........
+........#.....###.....................#.........#.........#.........#....##............#..##.............#.........#..#.......#....
+.#.........#....##..##.................#...#................................#...#.....#.........#.......#............#....#......#.
+..#.........#.......#..................#..#.#...#........#.#.......#...##.#........#..........#.#..........#..#.....#.........#....
+..#...............#...................##.#.......#...#..........#....................##.........#.................#..#......##..#..
+.#........#.......#............##...........##........#.......................#................#....................#...###......#.
+........###..........#..............#.............#..#.#.#............##...............#........#...#........#...................#.
+...#............................#...##.##........#......#..#...................#.#.....#...#.##...............#........#...#.......
+..#...##....................#.....##......#.......#..........#......#.........#...#..............#..............#..................
+.....#..#....................#....###.....#..#.............#...#....#................#.....#.....................#........#........
+.....#.#...#.....#..............##............#....##.#....#.#........##...........#....#.........................#....#......##...
+....#..#.....##...........#.#.#.#............#....#.....#.........#........................##.......#.#..............##...#........
+...............#..............#................................#....#........#.......#.......##......#.#............#......#....#..
+.#......#....##........#.............#..#.#.............#...#..#.........#.........#................#..................#...........
+.........#..............#....#......#.....##......#............#....#.........#....#...................#....#.........#......#..#..
+..............................#....#.#........#.#.....#..#.................#....#...#..........#............##.......#.#.#....#....
+.#..................#....#..#.......#.##..............#...#.......#................#...............................................
+.#..##.........................#.....###......#....#......#.....#............#.#......##......##......##....#..........##.....#....
+..........................##.#.....#..........................................#.#..#....#..#..................#...........#........
+..##.....#.......#....#.........#..........#....................#.........#........###........................#..........#.........
+.#.#...............#..........#.......#.....#....##.#..#.##...............#...#...#.#......#.......#.......#.#.............#....##.
+..................#...............##.........##..#........#..#..........#.....................#............................#.......
+.....#................#...##.......##.........#.....#.#....#.#........#...#..#....#..............#..#....#....#....#...............
+..##.#........#...............#.#..#...................##...#......#.#...#..#.....##.................##...#.#...................#..
+...#...............#......#.....#.......#......#.........#...#......#...#..#....#..#......#.......#.......#...#.##.#...........##..
+..............##..........##..........#..##...............#...........##..#..#..#.#.......#...#.............#......................
+..........#.#........................#...#.#..#.#...##..#.#.#.#.......#....#.#.#..............#...#...#........###..##...........#.
+......................#...#.#..##.....#....#.....###.#..#.....#..........#........#...........##...#..#...........##..#............
+..................................####.#..............#.................#........#.#............##......#.#..........#.............
+..................#..........#.............................#...........#..#..#......#................#.......##...##..#............
+....................#...#....#.#.#.##......#................#.................#...........#....#..........#....#...##.###..........
+.................#.......#...#............###.###..#.......#......#.......#..##......#.#.....#.....................#...............
+.................................................................S.................................................................
+.......##...........#.........###.......#....###.#.#....#.#....#....#........#.......#...#...#.#.........#...................#.....
+.......#...............#............#...#..#.......##...#...#.#............#.............#......##..........#..............#.......
+.......##.........#.....................##...#...#.................#...#.......#..####......#.....#..............#..##.............
+........#..#.............#.#..##..............#...#.............#.....#......#...#.#.......#...............##...##.................
+.........#..#...#..#.#..#..#...................##......#.....#..#...##..............#......#..........#.##...#.#.##.#..............
+..............#..........#....................................#.........#.......#..#............##................#................
+...........#...#.....#.........#....#..###....#...#.......#....#...............##.....#.......#.#.....#.#....#.#..#................
+..#...................#........###..............#.#................#...###...##.............#.###......#...#...#.....#..........#..
+.#.#............#.....#....###......................................#..........................#..................#................
+................#..#...#................#.................##.................##..........#.......#...#.............#...............
+.....##...........#....#.......#......#.#.....#.....#................#.....#.........#..#.................#........#........#......
+.#.#.............#..#.#..............#.....#..#.#.....#..#......#.........#.....#.#......#..#.......#.#......##............#..#....
+...................#............#....#...........#........#...................#.....##..............#........###...............#...
+......###..........###.#.......#.................................................#..#.........#.#...#.........#.#..........#.#.....
+..#.................#..#..#...#............#...#...#..##.#....##..#..................##.....#......#.........................#...#.
+......................#.#.....#.#...#.......##...........#...#....#.............#.......#.............#.#.#.#......................
+......#..#.#..........#....#.........#......#................#.........##.#....#.......#........#.#....................#......#....
+..#....#....#...............#..........#...#.#......#...................#.........#..#.#......#..#.........................##....#.
+..............#..........##......#.##...#...#.#................#...#..#.......#.#.....#........#...###..##.........#..##.........#.
+........##...........................##.......#.#..................#........#.......#.#........#.........................##....#...
+..#.#...........#.......................#.#.....#....#.....#...............####...#..............#...#....................#.#......
+.......#...#....#.#.......#####...##.....#.#.......#....#.#........#................................#.##..........##....#..#.......
+.........#.....#................##.#..................#.....................#...#................#.###.#.......###....#............
+............#.#....#........#....#..................#...##.............#............#.......#.....#..#............##...............
+....#.....#..........#..............#...#...#........##.....#.#....#....#........##.............................#.#.......#........
+..#..#.#.......#.................#................................#......##.#..#..............#.#................#...#.#...........
+.....#.....#........................#..#................#......#.......#.........###.#.#.........#.........#.....#.......#.........
+.......#.......................................#.......#...............#.#..###...#.#.##.......#...........#.#.....#.##........#...
+......##.........#.................................#.........#........##.#................#.#...#.............#...#..#........#....
+......#.....#.#.......#...........#..#...........#.........#..#.#.......#.........##.....#....#.#...............#...#...#....#...#.
+..#...#.#....#....#..............................#..#...#.......#.#.#..##..................#...............#......#..###..#.#......
+.....#...#..#......#.....##...............#..........#..#.#####.......#...........#...................#.....#...#.........#..#.#...
+.................#.......#..................#........#.......##...##.#....#.#.............#.............#....#....#................
+...........####..#.....#....#.............#.......#...#..#.....#.............#...#....#.............#.#....#.#.............#.......
+...#..#..#...#...#.#.....#.......................#....#..###.###.....#.........#....................#....#..#............#.....#...
+.#.##....##...#......#.#.....#......................#.##..................#........#..#................#.#.......#.............#...
+....##........#.......#..#..#............#..#..#..#...#......###..#..#..#...##...............................#.#........#......#.#.
+..#..#..........#..........#..#.#.............#.....#...........#.##.......#............................#...........#...#..........
+..#.#..#...#....#.....#.....#...#................#.....#.....#....#..#...#..#....#....#.....................#....#.................
+.......#........#...#.............#.................#...#.#.....#.#....#..........#......................#..#............#.........
+....#........#........#..............#.........................#...................#..........#.........#..#.........#.............
+................#........#.........#............................#.#.............#..##.......#......#..#.................#......#.#.
+..#.....#.........#...#..#.#.........................#...#...#...........#.....#...........#........#.............#.....#........#.
+....#...#....#......#....#...#..#.................#...##.....#.#............................##...#...#..##.#.....................#.
+...#..##...............#............................#...........#......#.#.....#............#........#.##................#.........
+................#..#.............#..#..............#.#....#...#.#...#...#.#.##.............................#..#...........#........
+.......#.......#....###............#.#.#.....................#.#..#....#.................##.....#.#..........##..#......#..........
+.......#..........##.#.......#.##...#...............##.....#..........#................#............#...#........#........#........
+...###.#.............................#.....#.#............##..#...#.....###..........#...............................#.....#....#..
+....###.#...#.......#.##........#......#..##.#..........#.#...#.#....#.#..............##....#..#...#...........#...#.#..#..........
+.....#....#.#..##.....#..........#..#...##..............#.......#.......#.............#..#.....#.......#.....#...##...###.......#..
+........##...#...##..#.#.....#..........................#.#.#..#..#...................#....#....#..#....#..........#....##.........
+...........##.....#...#........##..#........#....#..........#..#...............................................#......#.#.......#..
+...#..##.........##....#...........##...#.......##.........#........#...........#........#.#.##...........#....#.....###...#.......
+...#...#........................#..#...#..#........................................#......#..#...#.#....#...........#..............
+...#..#.......#..#......##...................#...............#.....#.#.............#.....#.........#.#..##.....#..........#..#.....
+....###....#..#.....#.#........#.##.......##...#...............#...............###.###.#...#............##.....#.................#.
+....#...#.........#.##............#.....#........#............................................##.#......#..##.........#....###..#..
+............#...##..#..........#........#.......#.#..........................#..#.#.......#......#.......................##.#..#...
+....#......#....#....#..#.....#........#......#....#..#.#..............................#..#....#............#....#.................
+..#.............#...#......#...#.....................#.##...............................##...#.......#........................#.##.
+....#....##........#..............#....#.......#.....................................#........#........#...##..........#...........
+....#.#.##..#..#....................#.................#.##.............#....#....#.............###...#...#..##....#.....##.........
+.............#.......#...............#........#.#.....#..#.#................#.....#..##.....#....#...............#....#......#...#.
+...................................................................................................................................

day21-easy/sample.in

@@ -0,0 +1,11 @@
+...........
+.....###.#.
+.###.##..#.
+..#.#...#..
+....#.#....
+.##..S####.
+.##..#...#.
+.......##..
+.##.#.####.
+.##..##.##.
+...........

day21-easy/src/main.zig

@@ -0,0 +1,102 @@
+const std = @import("std");
+
+const CellStatus = enum(u2) {
+    Rock = 0,
+    Reachable = 1,
+    ReachedEven = 2,
+    ReachedOdd = 3,
+};
+
+const Map = [256][256]CellStatus;
+
+fn solveMap(map: Map) usize {
+    const height = map.len;
+    const width = map[0].len;
+    var current_map = map;
+    for (0..64) |i| {
+        _ = i;
+        var next_map = current_map;
+        for (0..height) |row| {
+            for (0..width) |column| {
+                const maybe_next_status: ?CellStatus = switch (current_map[row][column]) {
+                    .ReachedEven => .ReachedOdd,
+                    .ReachedOdd => .ReachedEven,
+                    else => null,
+                };
+
+                if (maybe_next_status) |next_status| {
+                    if (row > 0 and next_map[row - 1][column] == .Reachable) {
+                        next_map[row - 1][column] = next_status;
+                    }
+
+                    if (row + 1 < height and next_map[row + 1][column] == .Reachable) {
+                        next_map[row + 1][column] = next_status;
+                    }
+
+                    if (column > 0 and next_map[row][column - 1] == .Reachable) {
+                        next_map[row][column - 1] = next_status;
+                    }
+
+                    if (column + 1 < width and next_map[row][column + 1] == .Reachable) {
+                        next_map[row][column + 1] = next_status;
+                    }
+                }
+            }
+        }
+
+        current_map = next_map;
+    }
+
+    var result: usize = 0;
+    for (0..height) |row| {
+        for (0..width) |column| {
+            if (current_map[row][column] == .ReachedEven) {
+                result += 1;
+            }
+        }
+    }
+
+    return result;
+}
+
+pub fn solveAll(reader: anytype) !usize {
+    var result: usize = 0;
+    while (true) {
+        var map = std.mem.zeroes(Map);
+
+        var row: usize = 0;
+        var empty_line_reached = false;
+        var line_buffer: [1000]u8 = undefined;
+        while (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')) |line| {
+            if (line.len == 0) {
+                empty_line_reached = true;
+                break;
+            }
+            for (line, 0..) |char, column| {
+                map[row][column] = switch (char) {
+                    '#' => .Rock,
+                    '.' => .Reachable,
+                    'S' => .ReachedEven,
+                    else => unreachable,
+                };
+            }
+            row += 1;
+        }
+
+        result += solveMap(map);
+
+        if (!empty_line_reached) {
+            return result;
+        }
+    }
+}
+
+pub fn main() !void {
+    const stdout = std.io.getStdOut().writer();
+
+    const raw_in = std.io.getStdIn();
+    var buffered_reader = std.io.bufferedReader(raw_in.reader());
+    var reader = buffered_reader.reader();
+    const result = try solveAll(&reader);
+    try stdout.print("{d}\n", .{result});
+}