day 22, part 2

day22-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 = "day22-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);
+}

day22-hard/sample.in

@@ -0,0 +1,7 @@
+1,0,1~1,2,1
+0,0,2~2,0,2
+0,2,3~2,2,3
+0,0,4~0,2,4
+2,0,5~2,2,5
+0,1,6~2,1,6
+1,1,8~1,1,9

day22-hard/src/main.zig

@@ -0,0 +1,229 @@
+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 readNumber(comptime T: type, line: []const u8, index: *usize) T {
+    var result: T = 0;
+    while (index.* < line.len) : (index.* += 1) {
+        const char = line[index.*];
+        switch (char) {
+            '0'...'9' => {
+                result = result * 10 + (char - '0');
+            },
+            else => {
+                break;
+            },
+        }
+    }
+
+    return result;
+}
+
+const Segment = packed struct(u32) {
+    first: u16,
+    last: u16,
+
+    fn init(a: u16, b: u16) Segment {
+        if (a < b) {
+            return .{
+                .first = a,
+                .last = b,
+            };
+        } else {
+            return .{
+                .first = b,
+                .last = a,
+            };
+        }
+    }
+
+    fn intersects(a: Segment, b: Segment) bool {
+        return a.first <= b.last and a.last >= b.first;
+    }
+};
+
+const Brick = struct {
+    x: Segment,
+    y: Segment,
+    z: Segment,
+    is_settled: bool,
+
+    fn is_above(self: *const Brick, other: Brick) bool {
+        return Segment.intersects(self.x, other.x) and Segment.intersects(self.y, other.y) and self.z.first > other.z.first;
+    }
+
+    fn is_on(self: *const Brick, other: Brick) bool {
+        return Segment.intersects(self.x, other.x) and Segment.intersects(self.y, other.y) and self.z.first == other.z.last + 1;
+    }
+
+    pub fn format(value: Brick, comptime _: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
+        return writer.print("{d},{d},{d}~{d},{d},{d}", .{ value.x.first, value.y.first, value.z.first, value.x.last, value.y.last, value.z.last });
+    }
+};
+
+fn settleBrick(bricks: []Brick, this: *Brick) usize {
+    if (this.is_settled) {
+        return 0;
+    }
+
+    var moved_bricks: usize = 0;
+    var min_z: u16 = 1;
+    for (bricks) |*other| {
+        if (this.is_above(other.*)) {
+            moved_bricks += settleBrick(bricks, other);
+            min_z = @max(min_z, other.z.last + 1);
+        }
+    }
+
+    if (this.z.first != min_z) {
+        moved_bricks += 1;
+    }
+
+    this.z.last -= (this.z.first - min_z);
+    this.z.first = min_z;
+    this.is_settled = true;
+    return moved_bricks;
+}
+
+fn settleBricks(bricks: []Brick) usize {
+    var result: usize = 0;
+
+    for (bricks) |*this| {
+        result += settleBrick(bricks, this);
+    }
+
+    return result;
+}
+
+fn simulateDisintegration(bricks: []const Brick, brick_number: usize) usize {
+    var simulated_bricks_array: [1500]Brick = undefined;
+    std.mem.copy(Brick, &simulated_bricks_array, bricks);
+    var simulated_bricks = simulated_bricks_array[0..bricks.len];
+
+    for (simulated_bricks) |*brick| {
+        brick.*.is_settled = false;
+    }
+
+    simulated_bricks[brick_number].z = Segment.init(0, 0);
+    simulated_bricks[brick_number].is_settled = true;
+
+    return settleBricks(simulated_bricks);
+}
+
+fn solveForBricks(bricks: []Brick) usize {
+    _ = settleBricks(bricks);
+
+    var result: usize = 0;
+    for (0..bricks.len) |brick_number| {
+        //std.debug.print("Simulating disintegration of brick {d}\n", .{brick_number});
+        result += simulateDisintegration(bricks, brick_number);
+    }
+
+    return result;
+}
+
+fn solveLines(lines: []const []const u8) usize {
+    var bricks_list = StackList(Brick, usize, 1500).init();
+
+    for (lines) |line| {
+        var i: usize = 0;
+        var x1 = readNumber(u16, line, &i);
+
+        i += 1;
+        var y1 = readNumber(u16, line, &i);
+
+        i += 1;
+        var z1 = readNumber(u16, line, &i);
+
+        i += 1;
+        var x2 = readNumber(u16, line, &i);
+
+        i += 1;
+        var y2 = readNumber(u16, line, &i);
+
+        i += 1;
+        var z2 = readNumber(u16, line, &i);
+
+        bricks_list.add(.{
+            .x = Segment.init(x1, x2),
+            .y = Segment.init(y1, y2),
+            .z = Segment.init(z1, z2),
+            .is_settled = false,
+        });
+    }
+
+    return solveForBricks(bricks_list.getMutableSlice());
+}
+
+pub fn solveAll(reader: anytype) !usize {
+    var result: usize = 0;
+    while (true) {
+        var allocator_buffer: [50000]u8 = undefined;
+        var fba = std.heap.FixedBufferAllocator.init(&allocator_buffer);
+        var allocator = fba.allocator();
+
+        var lines = StackList([]u8, usize, 1500).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});
+}