boost for parsing 2022-11

2022/11.cpp

@@ -6,79 +6,87 @@
 #include <string>
 #include <vector>
 
-#include <boost/range/irange.hpp>
+#include <boost/phoenix.hpp>
+#include <boost/range/adaptor/indexed.hpp>
+#include <boost/spirit/include/qi.hpp>
 
 #include <doctest.h>
 
+#include <aocpp/Parsing.hpp>
 #include <aocpp/Startup.hpp>
 
 namespace {
 
+namespace qi = boost::spirit::qi;
+namespace phx = boost::phoenix;
+
 struct Monkey {
   std::vector<std::int64_t> items;
   std::int64_t divisor;
   std::size_t true_ix, false_ix;
   std::optional<std::int64_t> rhs;
   char op;
+
+  auto throw_to(std::int64_t const item) const -> std::size_t {
+    return item % divisor == 0 ? true_ix : false_ix;
+  }
+
+  auto operation(std::int64_t const item) const -> std::int64_t {
+    auto const y = rhs.value_or(item);
+    switch (op) {
+      case '+': return item + y;
+      case '*': return item * y;
+      default: throw std::runtime_error{"bad input"};
+    }
+    return item;
+  }
 };
 
-auto Parse(std::istream & in) -> std::vector<Monkey>
-{
-  std::string word;
-  std::vector<Monkey> monkies;
+struct Grammar : public qi::grammar<std::string::const_iterator, std::vector<Monkey>()> {
+  qi::rule<iterator_type, Monkey()> monkey;
+  qi::rule<iterator_type, std::vector<Monkey>()> monkies;
 
-  while (in >> word) {
-    monkies.emplace_back();
-    Monkey & m = monkies.back();
-
-    in >> word >> word >> word; // 0: Starting items:
-
-    for (;;) {
-      std::int64_t elt;
-      in >> elt;
-      m.items.push_back(elt);
-
-      char c;
-      in >> c;
-      if (c != ',') break;
+  Grammar() : base_type{monkies} {
+    using namespace qi::labels;
+    monkies = monkey % "\n";
+    monkey =
+      "Monkey " >>
+      qi::omit[qi::ulong_long] >>
+      ":\n  Starting items: " >>
+      (qi::long_long % ", ") [ phx::bind(&Monkey::items, _val) = _1 ] >>
+      "\n  Operation: new = old " >>
+      qi::char_ [ phx::bind(&Monkey::op, _val) = _1 ] >>
+      " " >>
+      ("old" | qi::long_long [ phx::bind(&Monkey::rhs, _val) = _1 ]) >>
+      "\n  Test: divisible by " >>
+      qi::long_long [ phx::bind(&Monkey::divisor, _val) = _1 ] >>
+      "\n    If true: throw to monkey " >>
+      qi::ulong_long [ phx::bind(&Monkey::true_ix, _val) = _1 ] >>
+      "\n    If false: throw to monkey " >>
+      qi::ulong_long [ phx::bind(&Monkey::false_ix, _val) = _1 ] >>
+      "\n";
   }
-
-    in >> word >> word >> word >> word; // Operation: new = old
-
-    in >> m.op >> word;
-    if (word != "old") m.rhs = std::stoll(word);
-
-    in >> word >> word >> word >> m.divisor;
-    in >> word >> word >> word >> word >> word >> m.true_ix
-       >> word >> word >> word >> word >> word >> m.false_ix;
-  }
-
-  return monkies;
-}
+};
 
 auto Solve(std::vector<Monkey> const& input, std::size_t const rounds, std::optional<std::int64_t> const modulus) -> std::int64_t
 {
-  std::vector<std::int64_t> throws(input.size());
-  for (auto const i : boost::irange(input.size())) {
-    for (auto item : input[i].items) {
-      auto cursor = i;
+  auto throws = std::vector<std::int64_t>(input.size());
+  for (auto const& [start, monkey] : boost::adaptors::index(input)) {
+    for (auto item : monkey.items) {
+      auto cursor = static_cast<std::size_t>(start);
       for (auto n = rounds; n > 0;) {
         throws[cursor]++;
         auto const& m = input[cursor];
 
-        auto const y = m.rhs.value_or(item);
-        switch (m.op) {
-          case '+': item += y; break;
-          case '*': item *= y; break;
-          default: throw std::runtime_error{"bad input"};
-        }
-        if (modulus.has_value()) {
+        item = m.operation(item);
+
+        if (modulus) {
           item %= *modulus;
         } else {
           item /= 3;
         }
 
-        auto const next = (item % m.divisor == 0) ? m.true_ix : m.false_ix;
+        auto const next = m.throw_to(item);
         if (next < cursor) n--;
         cursor = next;
       }
@@ -100,9 +108,9 @@ auto Part2(std::vector<Monkey> const& input) -> std::int64_t
 {
   auto const modulus =
     std::transform_reduce(
-      input.cbegin(), input.cend(),
+      input.begin(), input.end(),
       std::int64_t{1}, std::lcm<std::int64_t, std::int64_t>,
-      [](Monkey const& m) { return m.divisor; });
+      [](auto const& m) { return m.divisor; });
   return Solve(input, 10'000, modulus);
 }
 
@@ -140,7 +148,7 @@ Monkey 3:
     If false: throw to monkey 1
 )"
     };
-    auto const input = Parse(in);
+    auto const input = aocpp::ParseGrammar(Grammar{}, in);
     CHECK(Part1(input) ==        10'605);
     CHECK(Part2(input) == 2'713'310'158);
   }
@@ -148,7 +156,7 @@ Monkey 3:
 
 auto Main(std::istream & in, std::ostream & out) -> void
 {
-  auto const input {Parse(in)};
+  auto const input = aocpp::ParseGrammar(Grammar{}, in);
   out << "Part 1: " << Part1(input) << std::endl;
   out << "Part 2: " << Part2(input) << std::endl;
 }