day 8, part 2 (too slow, does not produce an answer)

day08-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 = "day08-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);
+}

day08-hard/sample.in

@@ -0,0 +1,10 @@
+LR
+
+PPA = (PPB, XXX)
+PPB = (XXX, PPZ)
+PPZ = (PPB, XXX)
+QQA = (QQB, XXX)
+QQB = (QQC, QQC)
+QQC = (QQZ, QQZ)
+QQZ = (QQB, QQB)
+XXX = (XXX, XXX)

day08-hard/src/main.zig

@@ -0,0 +1,154 @@
+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: *const Self, needle: T) bool {
+            for (0..self.length) |i| {
+                if (self.mem[i] == needle) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        fn getMutableSlice(self: *Self) []T {
+            //var mem_full_slice = &self.mem;
+            //var mem_slice: []T = mem_full_slice[0..self.length];
+            //return mem_slice;
+            return (&self.mem)[0..self.length];
+        }
+
+        fn getLoopedValue(self: *const Self, index: usize) T {
+            return self.mem[index % self.length];
+        }
+
+        fn reset(self: *Self) void {
+            self.length = 0;
+        }
+
+        fn init() Self {
+            return Self{
+                .mem = undefined,
+                .length = 0,
+            };
+        }
+    };
+}
+
+const SIXTEEN_BITS = 65535;
+const FIVE_BITS = 31;
+const DEFAULT_NODE_VALUE = (SIXTEEN_BITS << 16) | SIXTEEN_BITS;
+
+const Directions = StackList(usize, usize, 1000);
+
+fn parseDirections(line: []const u8) Directions {
+    var result = Directions.init();
+
+    const left: usize = SIXTEEN_BITS << 16;
+    const right: usize = SIXTEEN_BITS;
+
+    var index: usize = 0;
+    while (index < line.len) : (index += 1) {
+        result.add(switch (line[index]) {
+            'L' => left,
+            'R' => right,
+            else => unreachable,
+        });
+    }
+
+    return result;
+}
+
+const Nodes = [32 * 32 * 32]usize;
+
+fn parseNodeNumber(line: []const u8) usize {
+    var result: usize = 0;
+    for (line) |char| {
+        result = (result << 5) + (char - 'A');
+    }
+
+    return result;
+}
+
+fn parseNodeLine(line: []const u8, state: *Nodes) void {
+    const current_node_number = parseNodeNumber(line[0..3]);
+    state[current_node_number] = (parseNodeNumber(line[7..10]) << 16) | parseNodeNumber(line[12..15]);
+}
+
+fn solve(nodes: Nodes, directions: Directions) usize {
+    var current = StackList(usize, usize, 1023).init();
+    {
+        var node_number: usize = 0;
+        while (node_number < nodes.len) : (node_number += 32) {
+            if (nodes[node_number] != DEFAULT_NODE_VALUE) {
+                current.add(node_number);
+            }
+        }
+    }
+
+    std.debug.print("Total number of starting points: {d}\n", .{current.length});
+
+    var i: usize = 0;
+    while (true) : (i += 1) {
+        if (i & SIXTEEN_BITS == 0) {
+            var debug_string = StackList(u8, u8, 255).init();
+            for (current.getMutableSlice()) |current_number| {
+                debug_string.add(@as(u8, @intCast((current_number >> 10) & FIVE_BITS)) + 'A');
+                debug_string.add(@as(u8, @intCast((current_number >> 5) & FIVE_BITS)) + 'A');
+                debug_string.add(@as(u8, @intCast((current_number >> 0) & FIVE_BITS)) + 'A');
+                debug_string.add(' ');
+            }
+            std.debug.print("Points at step {d}: {s}\n", .{ i, debug_string.getMutableSlice() });
+        }
+
+        var are_all_z = true;
+        for (current.getMutableSlice()) |*current_number| {
+            if (current_number.* & FIVE_BITS != 'Z' - 'A') {
+                are_all_z = false;
+            }
+
+            const mask = nodes[current_number.*] & directions.getLoopedValue(i);
+            current_number.* = (mask | (mask >> 16)) & SIXTEEN_BITS;
+        }
+
+        if (are_all_z) {
+            break;
+        }
+    }
+
+    return i;
+}
+
+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();
+
+    var line_buffer: [1000]u8 = undefined;
+    const first_line = (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')).?;
+    var directions = parseDirections(first_line);
+    _ = try reader.readUntilDelimiterOrEof(&line_buffer, '\n');
+
+    var nodes: Nodes = undefined;
+    for (&nodes) |*node| {
+        node.* = DEFAULT_NODE_VALUE;
+    }
+    while (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')) |line| {
+        parseNodeLine(line, &nodes);
+    }
+
+    const result = solve(nodes, directions);
+    try stdout.print("{d}\n", .{result});
+}