day 13, part 2

day13-hard/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 = "day13-hard",
+        // 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);
+}

day13-hard/sample.in

@@ -0,0 +1,15 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#

day13-hard/src/main.zig

@@ -0,0 +1,150 @@
+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 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 isMirroredHorizontallyAt(lines: []const []const u8, mirror_before: usize) bool {
+    var differences: u8 = 0;
+
+    var a = mirror_before - 1;
+    var b = mirror_before;
+
+    while (a >= 0 and b < lines.len) {
+        for (lines[a], lines[b]) |char_a, char_b| {
+            if (char_a != char_b) {
+                differences += 1;
+                if (differences > 1) {
+                    return false;
+                }
+            }
+        }
+
+        if (a == 0) {
+            break;
+        }
+        a -= 1;
+
+        b += 1;
+    }
+
+    return differences == 1;
+}
+
+fn isMirroredVerticallyAt(lines: []const []const u8, mirror_before: usize) bool {
+    var differences: u8 = 0;
+
+    for (lines) |line| {
+        var a = mirror_before - 1;
+        var b = mirror_before;
+
+        while (a >= 0 and b < line.len) {
+            if (line[a] != line[b]) {
+                differences += 1;
+                if (differences > 1) {
+                    return false;
+                }
+            }
+
+            if (a == 0) {
+                break;
+            }
+            a -= 1;
+
+            b += 1;
+        }
+    }
+
+    return differences == 1;
+}
+
+fn solveLines(lines: []const []const u8) usize {
+    var result: usize = 0;
+
+    var column: usize = 1;
+    while (column < lines[0].len) : (column += 1) {
+        if (isMirroredVerticallyAt(lines, column)) {
+            result += column;
+        }
+    }
+
+    var row: usize = 1;
+    while (row < lines.len) : (row += 1) {
+        if (isMirroredHorizontallyAt(lines, row)) {
+            result += 100 * row;
+        }
+    }
+
+    return result;
+}
+
+pub fn solveAll(reader: anytype) !usize {
+    var result: usize = 0;
+    while (true) {
+        var allocator_buffer: [10000]u8 = undefined;
+        var fba = std.heap.FixedBufferAllocator.init(&allocator_buffer);
+        var allocator = fba.allocator();
+
+        var lines = StackList([]const u8, usize, 100).init();
+        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;
+            }
+            lines.add(try allocator.dupe(u8, line));
+        }
+
+        result += solveLines(lines.getSlice());
+
+        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});
+}