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day19.zig
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usingnamespace @import("util.zig");
pub fn runPart1(r: anytype) !usize {
var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
defer arena.deinit();
const rules = try parseRules(r, &arena.allocator);
return countValid(r, rules, &arena.allocator);
}
pub fn runPart2(r: anytype) !usize {
var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
defer arena.deinit();
var rules = try parseRules(r, &arena.allocator);
// Rewrite with:
// 8: 42 | 42 8
// 11: 42 31 | 42 11 31
var res = try rules.getOrPut(8);
res.entry.value = Rule{ .Alt = &[_][]const usize{ &[_]usize{42}, &[_]usize{ 42, 8 } } };
res = try rules.getOrPut(11);
res.entry.value = Rule{ .Alt = &[_][]const usize{ &[_]usize{ 42, 31 }, &[_]usize{ 42, 11, 31 } } };
return countValid(r, rules, &arena.allocator);
}
const Rule = union(enum) {
Char: u8,
Alt: []const []const usize,
};
const RuleMap = std.AutoHashMap(usize, Rule);
fn countValid(r: anytype, rules: RuleMap, a: *Allocator) !usize {
var buf: [100]u8 = undefined;
var cnt: usize = 0;
while (true) {
const line = (try r.readUntilDelimiterOrEof(&buf, '\n')) orelse return cnt;
const is_valid = try isMessageValid(line, rules, a);
cnt += @boolToInt(is_valid);
}
return cnt;
}
// Caller owns returned map.
fn parseRules(r: anytype, a: *Allocator) !RuleMap {
var buf: [100]u8 = undefined;
var rules = std.AutoHashMap(usize, Rule).init(a);
while (true) {
var line = (try r.readUntilDelimiterOrEof(&buf, '\n')) orelse return error.InvalidInput;
if (0 == line.len)
break;
const start = mem.indexOf(u8, line, ": ") orelse return error.InvalidInput;
const rule_index = try fmt.parseUnsigned(usize, line[0..start], 10);
line = line[start + 2 ..];
if (mem.startsWith(u8, line, "\"")) {
try rules.put(rule_index, Rule{ .Char = line[1] });
continue;
}
var iter = mem.split(line, "|");
var rule = ArrayList([]usize).init(a);
defer rule.deinit();
while (iter.next()) |s| {
var nums = mem.split(s, " ");
var single = ArrayList(usize).init(a);
defer single.deinit();
while (nums.next()) |num| {
if (0 == num.len)
continue;
const n = try fmt.parseUnsigned(usize, num, 10);
try single.append(n);
}
try rule.append(single.toOwnedSlice());
}
try rules.put(rule_index, Rule{ .Alt = rule.toOwnedSlice() });
}
return rules;
}
/// Checks if message satisfies first rule.
fn isMessageValid(line: []const u8, rules: RuleMap, a: *Allocator) !bool {
const rule0 = rules.get(0).?;
const result = (try checkRule(line, rule0, rules, a)) orelse return false;
for (result) |last| {
if (last == line.len)
return true;
}
return false;
}
var debug: bool = false;
fn checkRule(msg: []const u8, r: Rule, rs: RuleMap, a: *Allocator) anyerror!?[]usize {
if (msg.len == 0)
return null;
switch (r) {
.Char => {
if (msg[0] != r.Char)
return null;
const res = try a.alloc(usize, 1);
res[0] = 1;
return res;
},
.Alt => {
var good = ArrayList(usize).init(a);
defer good.deinit();
loop: for (r.Alt) |list, i| {
var curr: []const usize = &[_]usize{0};
for (list) |num| {
if (curr.len == 0)
continue :loop;
const rule_to_check = rs.get(num) orelse unreachable;
var next = ArrayList(usize).init(a);
defer next.deinit();
for (curr) |c| {
const indices = (try checkRule(msg[c..], rule_to_check, rs, a)) orelse continue;
for (indices) |ind| {
try next.append(c + ind);
}
}
curr = next.toOwnedSlice();
}
for (curr) |ind| {
try good.append(ind);
}
}
return good.toOwnedSlice();
},
}
}
test "part 1" {
const input =
\\0: 4 1 5
\\1: 2 3 | 3 2
\\2: 4 4 | 5 5
\\3: 4 5 | 5 4
\\4: "a"
\\5: "b"
\\
\\ababbb
\\bababa
\\abbbab
\\aaabbb
\\aaaabbb
;
var r = io.fixedBufferStream(input).reader();
expectEqual(@as(usize, 2), try runPart1(r));
}
test "part 2" {
const input =
\\42: 9 14 | 10 1
\\9: 14 27 | 1 26
\\10: 23 14 | 28 1
\\1: "a"
\\11: 42 31
\\5: 1 14 | 15 1
\\19: 14 1 | 14 14
\\12: 24 14 | 19 1
\\16: 15 1 | 14 14
\\31: 14 17 | 1 13
\\6: 14 14 | 1 14
\\2: 1 24 | 14 4
\\0: 8 11
\\13: 14 3 | 1 12
\\15: 1 | 14
\\17: 14 2 | 1 7
\\23: 25 1 | 22 14
\\28: 16 1
\\4: 1 1
\\20: 14 14 | 1 15
\\3: 5 14 | 16 1
\\27: 1 6 | 14 18
\\14: "b"
\\21: 14 1 | 1 14
\\25: 1 1 | 1 14
\\22: 14 14
\\8: 42
\\26: 14 22 | 1 20
\\18: 15 15
\\7: 14 5 | 1 21
\\24: 14 1
\\
\\abbbbbabbbaaaababbaabbbbabababbbabbbbbbabaaaa
\\bbabbbbaabaabba
\\babbbbaabbbbbabbbbbbaabaaabaaa
\\aaabbbbbbaaaabaababaabababbabaaabbababababaaa
\\bbbbbbbaaaabbbbaaabbabaaa
\\bbbababbbbaaaaaaaabbababaaababaabab
\\ababaaaaaabaaab
\\ababaaaaabbbaba
\\baabbaaaabbaaaababbaababb
\\abbbbabbbbaaaababbbbbbaaaababb
\\aaaaabbaabaaaaababaa
\\aaaabbaaaabbaaa
\\aaaabbaabbaaaaaaabbbabbbaaabbaabaaa
\\babaaabbbaaabaababbaabababaaab
\\aabbbbbaabbbaaaaaabbbbbababaaaaabbaaabba
;
var r = io.fixedBufferStream(input).reader();
expectEqual(@as(usize, 3), try runPart1(r));
r = io.fixedBufferStream(input).reader();
expectEqual(@as(usize, 12), try runPart2(r));
}