2024 Day 24 Part 2
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08c71c07d4
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1 changed files with 253 additions and 21 deletions
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@ -16,6 +16,11 @@ pub fn main() !void {
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const text = try aoc.readAll(allocator, "input/day24.txt");
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defer allocator.free(text);
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const text2 = try aoc.readAll(allocator, "input/day24_swaps.txt");
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defer allocator.free(text2);
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const swaps = try aoc.parseAll(Swap, allocator, text2, "\n");
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defer swaps.deinit();
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var blocks = std.mem.tokenizeSequence(u8, text, "\n\n");
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var inputs = try aoc.parseAll(Input, allocator, blocks.next().?, "\n");
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@ -29,6 +34,12 @@ pub fn main() !void {
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try stdout.print("{}\n", .{try part1(allocator, inputs.items, gates.items)});
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try bw.flush();
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var wires = try part2(allocator, gates.items, swaps.items);
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defer wires.deinit();
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try stdout.print("{s}\n", .{wires.items});
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try bw.flush();
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}
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const String = []const u8;
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@ -49,6 +60,21 @@ const Input = struct {
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}
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};
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const Swap = struct {
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a: String,
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b: String,
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pub fn parse(_: Allocator, line: String) !Swap {
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var fields = std.mem.tokenizeSequence(u8, line, " ");
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const a = fields.next().?;
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const b = fields.next().?;
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return Swap{
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.a = a,
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.b = b,
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};
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}
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};
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const Gate = struct {
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a: String,
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b: String,
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@ -57,12 +83,18 @@ const Gate = struct {
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pub fn parse(_: Allocator, line: String) !Gate {
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var fields = std.mem.tokenizeSequence(u8, line, " ");
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const a = fields.next().?;
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var a = fields.next().?;
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const op = fields.next().?;
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const b = fields.next().?;
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var b = fields.next().?;
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if (!std.mem.eql(u8, fields.next().?, "->")) unreachable;
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const out = fields.next().?;
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if (std.mem.lessThan(u8, b, a)) {
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const t = a;
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a = b;
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b = t;
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}
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return Gate{
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.a = a,
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.b = b,
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@ -70,6 +102,31 @@ const Gate = struct {
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.op = Op.parse(op).?,
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};
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}
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pub fn format(
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self: Gate,
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comptime _: []const u8,
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_: std.fmt.FormatOptions,
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writer: anytype,
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) !void {
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try writer.print("{s} {s} {s} -> {s}", .{ self.a, self.op, self.b, self.out });
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}
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fn hasInputs(self: Gate, a: String, b: String) bool {
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return (streq(self.a, a) and streq(self.b, b)) or (streq(self.a, b) and streq(self.b, a));
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}
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fn hasOutput(self: Gate, out: String) bool {
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return streq(self.out, out);
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}
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fn mustOutput(self: Gate, out: String) Gate {
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if (self.hasOutput(out)) {
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return self;
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}
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std.debug.print("want: {s}, got: {s}\n", .{ out, self.out });
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unreachable;
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}
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};
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const Op = enum {
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@ -92,34 +149,26 @@ const Op = enum {
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.Xor => a ^ b,
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};
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}
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pub fn format(
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self: Op,
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comptime _: []const u8,
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_: std.fmt.FormatOptions,
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writer: anytype,
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) !void {
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const s = switch (self) {
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.And => "AND",
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.Or => "_OR",
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.Xor => "XOR",
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};
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try writer.print("{s}", .{s});
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}
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};
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fn part1(allocator: Allocator, inputs: []const Input, gates: []const Gate) !u64 {
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var values = StringMap(u1).init(allocator);
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var values = try eval(allocator, gates, inputs);
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defer values.deinit();
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for (inputs) |i| {
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try values.put(i.name, i.value);
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}
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var pending = List(Gate).init(allocator);
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try pending.appendSlice(gates);
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while (pending.items.len > 0) {
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var next = List(Gate).init(allocator);
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for (pending.items) |g| {
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if (values.contains(g.a) and values.contains(g.b)) {
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const a = values.get(g.a).?;
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const b = values.get(g.b).?;
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try values.put(g.out, g.op.eval(a, b));
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} else {
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try next.append(g);
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}
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}
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pending.deinit();
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pending = next;
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}
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var outputs = List(String).init(allocator);
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defer outputs.deinit();
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{
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@ -132,6 +181,7 @@ fn part1(allocator: Allocator, inputs: []const Input, gates: []const Gate) !u64
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}
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}
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std.mem.sort(String, outputs.items, {}, gtString);
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if (outputs.items.len != 46) unreachable;
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var n: u64 = 0;
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for (outputs.items) |z| {
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@ -143,6 +193,188 @@ fn part1(allocator: Allocator, inputs: []const Input, gates: []const Gate) !u64
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return n;
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}
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fn eval(allocator: Allocator, gates: []const Gate, inputs: []const Input) !StringMap(u1) {
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var values = StringMap(u1).init(allocator);
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for (inputs) |i| {
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try values.put(i.name, i.value);
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}
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var pending = List(Gate).init(allocator);
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try pending.appendSlice(gates);
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while (pending.items.len > 0) {
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var next = List(Gate).init(allocator);
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var changed = false;
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for (pending.items) |g| {
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if (values.contains(g.a) and values.contains(g.b)) {
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const a = values.get(g.a).?;
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const b = values.get(g.b).?;
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try values.put(g.out, g.op.eval(a, b));
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changed = true;
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} else {
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try next.append(g);
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}
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}
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if (!changed) {
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// No progress, drop everything and quit.
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pending.deinit();
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next.deinit();
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break;
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}
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pending.deinit();
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pending = next;
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}
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return values;
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}
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fn ltString(_: void, a: String, b: String) bool {
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return std.mem.lessThan(u8, a, b);
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}
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fn gtString(_: void, a: String, b: String) bool {
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return std.mem.lessThan(u8, b, a);
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}
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fn streq(a: String, b: String) bool {
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return std.mem.eql(u8, a, b);
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}
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fn part2(allocator: Allocator, circuit: []const Gate, swaps: []const Swap) !List(u8) {
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if (swaps.len == 4) {
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return try formatWires(allocator, swaps);
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}
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var renames = StringMap(String).init(allocator);
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defer renames.deinit();
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for (swaps) |swap| {
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try renames.put(swap.a, swap.b);
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try renames.put(swap.b, swap.a);
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}
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var fixed = List(Gate).init(allocator);
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defer fixed.deinit();
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for (circuit) |g| {
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try fixed.append(Gate{
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.out = renames.get(g.out) orelse g.out,
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.a = g.a,
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.b = g.b,
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.op = g.op,
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});
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}
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const gates = fixed.items;
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var arena = std.heap.ArenaAllocator.init(allocator);
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defer arena.deinit();
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const str = arena.allocator();
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// Assumption: Each input wire is used in exactly one one-bit adder.
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// Assumption: The input wires are never OR-ed directly for carries.
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for (0..45) |i| {
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const x = try std.fmt.allocPrint(str, "x{d:0>2}", .{i});
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const y = try std.fmt.allocPrint(str, "y{d:0>2}", .{i});
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var xors: usize = 0;
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var ands: usize = 0;
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for (gates) |g| {
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if (!g.hasInputs(x, y)) continue;
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if (g.op == .Xor) xors += 1;
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if (g.op == .And) ands += 1;
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if (g.op == .Or) unreachable;
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}
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if (xors != 1) unreachable;
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if (ands != 1) unreachable;
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}
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const lambda = struct {
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fn findGate(gs: []const Gate, i: String, j: String, op: Op) ?Gate {
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return for (gs) |g| {
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if (g.hasInputs(i, j) and g.op == op) break g;
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} else null;
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}
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fn findAdder(gs: []const Gate, i: String, j: String) ?struct { Gate, Gate } {
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const lo = for (gs) |g| {
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if (g.hasInputs(i, j) and g.op == .Xor) {
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break g;
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}
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} else return null;
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const hi = for (gs) |g| {
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if (g.hasInputs(i, j) and g.op == .And) {
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break g;
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}
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} else return null;
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return .{ lo, hi };
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}
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};
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// 00
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const a00, const b00 = lambda.findAdder(gates, "x00", "y00") orelse unreachable;
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std.debug.print("> a00 : {s}\n", .{a00});
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std.debug.print("> b00 : {s}\n", .{b00});
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const z00 = a00.mustOutput("z00");
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const c00 = b00;
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std.debug.print("> c00 : {s}\n", .{c00});
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std.debug.print("> z00 : {s}\n", .{z00});
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// 01 - end
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var c = List(String).init(allocator);
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defer c.deinit();
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try c.append(c00.out);
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for (1..45) |i| {
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const x = try std.fmt.allocPrint(str, "x{d:0>2}", .{i});
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const y = try std.fmt.allocPrint(str, "y{d:0>2}", .{i});
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const z = try std.fmt.allocPrint(str, "z{d:0>2}", .{i});
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const a, const b = lambda.findAdder(gates, x, y) orelse unreachable;
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std.debug.print("> a{d:0>2} : {s}\n", .{ i, a });
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std.debug.print("> b{d:0>2} : {s}\n", .{ i, b });
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const d, const e = lambda.findAdder(gates, c.items[i - 1], a.out) orelse unreachable;
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std.debug.print("> d{d:0>2} : {s}\n", .{ i, d });
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std.debug.print("> e{d:0>2} : {s}\n", .{ i, e });
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const zz = d.mustOutput(z);
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std.debug.print("> z{d:0>2} : {s}\n", .{ i, zz });
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const cc = lambda.findGate(gates, e.out, b.out, .Or) orelse unreachable;
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std.debug.print("> c{d:0>2} : {s}\n", .{ i, cc });
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try c.append(cc.out);
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}
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unreachable;
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}
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fn formatWires(allocator: Allocator, swaps: []const Swap) !List(u8) {
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var names = List(String).init(allocator);
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defer names.deinit();
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for (swaps) |swap| {
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try names.append(swap.a);
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try names.append(swap.b);
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}
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std.mem.sort(String, names.items, {}, ltString);
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var buf = List(u8).init(allocator);
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var w = buf.writer();
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if (names.items.len > 0) {
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try w.print("{s}", .{names.items[0]});
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}
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if (names.items.len > 1) {
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for (names.items[1..]) |n| {
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try w.print(",{s}", .{n});
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}
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}
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return buf;
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}
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