You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.

69 lines
1.4 KiB

require "advent"
rlines, _, strings = input(2020, 19).partition("\n\n")
strings = strings.lines
rules = {} of String => String
rlines.lines.map do |l|
rule, _, text = l.partition(": ")
rules[rule] = text
end
alias Matcher = Proc(String,Int32,Array(Int32))
def char(c)
->(str : String, i : Int32) { str[i]? == c ? [i+1] : [] of Int32 }
end
def any(ps)
->(str : String, i : Int32) { ps.flat_map { |p| p.call(str, i) } }
end
def seq(ps)
->(str : String, i : Int32) {
base = [i]
ps.each do |p|
base = base.flat_map { |i| p.call(str, i) }
end
base
}
end
def to_regex(rules, rule)
end
def build_rule(rules, built, rule) : Matcher
if exists = built[rule]?
return exists
end
body = rules[rule]
return built[rule] = char body[1] if body.matches? /"."/
branches = [] of Matcher
top = any(branches)
built[rule] = top
branches.concat(body.split(" | ").map { |b| seq(b.split(" ").map { |subrule| build_rule(rules, built, subrule) }) })
top
end
def part1(input)
rules, lines = input
matcher = build_rule(rules, {} of String => Matcher, "0")
lines.count do |l|
matcher.call(l, 0).includes? l.size
end
end
def part2(input)
rules, lines = input
rules["8"] = "42 | 42 8"
rules["11"] = "42 31 | 42 11 31"
matcher = build_rule(rules, {} of String => Matcher, "0")
lines.count do |l|
matcher.call(l, 0).includes? l.size
end
end
puts part1({rules,strings})
puts part2({rules,strings})