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const std = @import("std");
const aoc = @import("aoc");
const Rule = union(enum) {
c: u8,
combos: []const []const usize,
};
fn printSlice(slice: []const usize) void {
for (slice) |v, i| {
if (i > 0) {
aoc.debugfmt(" ", .{});
}
aoc.debugfmt("{}", .{v});
}
}
var stacktrace: std.ArrayList(usize) = undefined;
fn checkRule(rules: *std.AutoHashMap(usize, Rule), rid: usize, msg: []const u8, nextstack: *std.ArrayList(usize)) anyerror!bool {
if (msg.len == 0) return true;
const rule = rules.get(rid) orelse return aoc.Error.InvalidInput;
if (rule == .c) {
if (msg[0] != rule.c) return false;
if (msg.len == 1) return (nextstack.items.len == 0);
if (nextstack.items.len == 0) return false;
const next = nextstack.pop();
const valid = try checkRule(rules, next, msg[1..], nextstack);
if (valid) try stacktrace.append(next);
if (valid) return true;
try nextstack.append(next);
} else {
for (rule.combos) |ruleseq| {
try nextstack.appendSlice(ruleseq[1..]);
std.mem.reverse(usize, nextstack.items[nextstack.items.len - (ruleseq.len - 1) ..]);
const valid = try checkRule(rules, ruleseq[0], msg, nextstack);
if (valid) try stacktrace.append(ruleseq[0]);
if (valid) return true;
try nextstack.resize(nextstack.items.len - (ruleseq.len - 1));
}
}
return false;
}
fn freeRules(allocator: std.mem.Allocator, rules: *std.AutoHashMap(usize, Rule), ignore: ?[]const usize) void {
var mapit = rules.iterator();
while (mapit.next()) |kv| {
if (ignore != null and std.mem.indexOfScalar(usize, ignore.?, kv.key_ptr.*) != null) continue;
if (kv.value_ptr.* == .combos) {
for (kv.value_ptr.combos) |rs| {
allocator.free(rs);
}
allocator.free(kv.value_ptr.combos);
}
}
rules.deinit();
}
fn parseRule(allocator: std.mem.Allocator, rules: *std.AutoHashMap(usize, Rule), line: []const u8) !void {
const indexsep = try aoc.unwrap(std.mem.indexOf(u8, line, ": "));
const index = try std.fmt.parseInt(usize, line[0..indexsep], 10);
var chrsep = std.mem.indexOf(u8, line, "\"");
if (chrsep != null) {
if (chrsep.? == line.len - 1) return aoc.Error.InvalidInput;
try rules.put(index, Rule{ .c = line[chrsep.? + 1] });
} else {
var vals = std.ArrayList([]usize).init(allocator);
errdefer vals.deinit();
var ruleit = std.mem.split(u8, line[indexsep + 2 ..], " | ");
while (ruleit.next()) |r| {
var ruleids = std.ArrayList(usize).init(allocator);
errdefer ruleids.deinit();
var spaceit = std.mem.tokenize(u8, r, " ");
while (spaceit.next()) |word| {
try ruleids.append(try std.fmt.parseInt(usize, word, 10));
}
if (ruleids.items.len == 0) return aoc.Error.InvalidInput;
try vals.append(ruleids.items);
}
try rules.put(index, Rule{ .combos = vals.items });
}
}
fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
_ = args;
var rules = std.AutoHashMap(usize, Rule).init(allocator);
defer freeRules(allocator, &rules, null);
var partit = std.mem.split(u8, input, "\n\n");
var lineit = std.mem.tokenize(u8, try aoc.unwrap(partit.next()), "\n");
while (lineit.next()) |line| {
try parseRule(allocator, &rules, line);
}
var answer: u32 = 0;
var nextstack = std.ArrayList(usize).init(allocator);
defer nextstack.deinit();
stacktrace = std.ArrayList(usize).init(allocator);
defer stacktrace.deinit();
lineit = std.mem.tokenize(u8, try aoc.unwrap(partit.next()), "\n");
var count: usize = 0;
while (lineit.next()) |line| {
count += 1;
if (try checkRule(&rules, 0, line, &nextstack))
answer += 1;
try nextstack.resize(0);
}
return try std.fmt.allocPrint(allocator, "{}", .{answer});
}
fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
_ = args;
var rules = std.AutoHashMap(usize, Rule).init(allocator);
defer freeRules(allocator, &rules, ([_]usize{ 8, 11 })[0..]);
var partit = std.mem.split(u8, input, "\n\n");
var lineit = std.mem.tokenize(u8, try aoc.unwrap(partit.next()), "\n");
while (lineit.next()) |line| {
if (std.mem.eql(u8, line[0..2], "8:")) {
const p1: []const usize = ([_]usize{42})[0..];
const p2: []const usize = ([_]usize{ 42, 8 })[0..];
try rules.put(8, Rule{ .combos = ([_][]const usize{ p1, p2 })[0..] });
} else if (std.mem.eql(u8, line[0..3], "11:")) {
const p1: []const usize = ([_]usize{ 42, 31 })[0..];
const p2: []const usize = ([_]usize{ 42, 11, 31 })[0..];
try rules.put(11, Rule{ .combos = ([_][]const usize{ p1, p2 })[0..] });
} else {
try parseRule(allocator, &rules, line);
}
}
var answer: u32 = 0;
var nextstack = std.ArrayList(usize).init(allocator);
defer nextstack.deinit();
stacktrace = std.ArrayList(usize).init(allocator);
defer stacktrace.deinit();
var count: usize = 0;
lineit = std.mem.tokenize(u8, try aoc.unwrap(partit.next()), "\n");
while (lineit.next()) |line| {
count += 1;
const valid = try checkRule(&rules, 0, line, &nextstack);
answer += @boolToInt(valid);
if (aoc.debug) {
aoc.debugfmt("TRACE: [", .{});
std.mem.reverse(usize, stacktrace.items);
printSlice(stacktrace.items);
aoc.debugfmt("]\n", .{});
if (valid) {
aoc.debugfmt("MATCH {s}\n\n", .{line});
} else {
aoc.debugfmt("NO MATCH {s}\n\n", .{line});
}
}
try nextstack.resize(0);
}
return try std.fmt.allocPrint(allocator, "{}", .{answer});
}
pub const main = aoc.main(part1, part2, .{ "134", "377" });
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