qi parser for 13

2022/13.cpp

@@ -1,3 +1,4 @@
+#include <array>
 #include <cstdint>
 #include <iostream>
 #include <set>
@@ -11,21 +12,28 @@
 #include <aocpp/Startup.hpp>
 #include <aocpp/Overloaded.hpp>
 
+#include <boost/spirit/include/qi.hpp>
+#include <boost/phoenix.hpp>
+#include <boost/range/irange.hpp>
+
 namespace {
 
+namespace phx = boost::phoenix;
+namespace qi = boost::spirit::qi;
+
+struct Tree;
+using Trees = std::vector<Tree>;
+using Input = std::vector<std::array<Tree, 2>>;
+
 struct Tree {
-  std::variant<std::int64_t, std::vector<Tree>> rep;
+  std::variant<std::int64_t, Trees> rep;
 };
 
-auto operator<(Tree const& lhs, Tree const& rhs) -> bool;
-
-auto operator<(std::vector<Tree> const& x, std::int64_t y) -> bool;
-auto operator<(std::int64_t x, std::vector<Tree> const& y) -> bool;
 
 auto operator<(Tree const& x, std::int64_t y) -> bool;
 auto operator<(std::int64_t x, Tree const& y) -> bool;
 
-auto operator<(std::int64_t x, std::vector<Tree> const& y) -> bool {
+auto operator<(std::int64_t x, Trees const& y) -> bool {
   switch (y.size()) {
     case 0: return false;
     case 1: return x < y[0];
@@ -33,7 +41,7 @@ auto operator<(std::int64_t x, std::vector<Tree> const& y) -> bool {
   }
 }
 
-auto operator<(std::vector<Tree> const& x, std::int64_t y) -> bool {
+auto operator<(Trees const& x, std::int64_t y) -> bool {
   switch (x.size()) {
     case 0: return true;
     default: return x[0] < y;
@@ -52,68 +60,67 @@ auto operator<(Tree const& lhs, Tree const& rhs) -> bool {
   return std::visit(std::less(), lhs.rep, rhs.rep);
 }
 
-using Input = std::vector<Tree>;
+template <typename It>
+class Grammar : public qi::grammar<It, Input()> {
+  qi::rule<It, std::int64_t> leaf;
+  qi::rule<It, Trees()> trees;
+  qi::rule<It, Tree()> tree;
+  qi::rule<It, std::array<Tree, 2>()> treepair; 
+  qi::rule<It, Input()> input;
 
-auto ParseTree(std::string::iterator & begin, std::string::iterator end) -> Tree
-{
-  if (*begin == '[') {
-    begin++;
-    if (*begin == ']') {
-      begin++;
-      return Tree{std::vector<Tree>{}};
-    }
-    std::vector<Tree> subtrees;
-    top: subtrees.emplace_back(ParseTree(begin, end));
-    switch (*begin++) {
-      case ',': goto top;
-      case ']': return Tree{std::move(subtrees)};
-      default: throw std::runtime_error{"bad tree list"};
-    }
-  } else if (isdigit(*begin)) {
-    auto number_end = std::find_if_not(begin, end, isdigit);
-    std::string number_str {begin, number_end};
-    begin = number_end;
-    std::int64_t number = std::stoll(number_str);
-    return Tree{number};
-  } else {
-    throw std::runtime_error{"bad tree start"};
+public:
+  Grammar() : Grammar::base_type{input} {
+    using namespace qi::labels;
+
+    leaf  = qi::long_long;
+    trees = "[" >> -(tree % ",") >> "]";
+    tree  = leaf  [ bind(&Tree::rep, _val) = _1 ]
+          | trees [ bind(&Tree::rep, _val) = _1 ];
+    treepair = (tree >> "\n" >> tree >> "\n") [(_val[0] = _1, _val[1] = _2)];
+    input = -(treepair % "\n");
   }
-}
+};
 
 auto Parse(std::istream & in) -> Input
 {
   Input result;
-  std::string line;
-  while (std::getline(in, line)) {
-    auto cursor = line.begin();
-    result.push_back(ParseTree(cursor, line.end()));
-    std::getline(in, line);
-    cursor = line.begin();
-    result.push_back(ParseTree(cursor, line.end()));
-    std::getline(in, line); // skip blank
+  std::string content {std::istreambuf_iterator{in}, {}};
+  auto b {content.begin()};
+  auto const e {content.end()};
+
+  if (!qi::parse(b, e, Grammar<decltype(b)>{}, result) || b != e) {
+    throw std::runtime_error{"tree parser failed"};
   }
 
   return result;
 }
 
-auto Part1(Input const& input) -> std::int64_t
+auto Part1(Input const& input) -> std::size_t
 {
   std::int64_t result {0};
-  for (std::size_t i = 0; i < input.size(); i += 2) {
-    if (input[i] < input[i+1]) {
-      result += i/2 + 1;
+  for (auto const i : boost::irange(input.size())) {
+    if (input[i][0] < input[i][1]) {
+      result += i + 1;
     }
   }
   return result;
 }
 
-auto Part2(Input const& input) -> std::int64_t
+auto Part2(Input const& input) -> std::size_t
 {
-  Tree two {std::vector{Tree{std::vector{Tree{2}}}}};
-  Tree six {std::vector{Tree{std::vector{Tree{6}}}}};
-  auto ix2 = std::count_if(input.begin(), input.end(), [&](auto const& x) { return x < two; });
-  auto ix6 = std::count_if(input.begin(), input.end(), [&](auto const& x) { return x < six; });
-  return (ix2+1) * (ix6+2);
+  Tree two{2}, six{6}; // Indistinguishable from [[2]] and [[6]]
+  std::size_t ix2{1}, ix6{2};
+  for (auto const& pair : input) {
+    for (auto const& tree : pair) {
+      if (tree < six) {
+        ix6++;
+        if (tree < two) {
+          ix2++;
+        }
+      }
+    }
+  }
+  return ix2 * ix6;
 }
 
 } // namespace
@@ -122,11 +129,11 @@ TEST_SUITE("2022-13 examples") {
   TEST_CASE("simple ordering") {
     CHECK(Tree{1} < Tree{2});
     CHECK(!(Tree{2} < Tree{1}));
-    CHECK(Tree{std::vector{Tree{1}}} < Tree{std::vector{Tree{2}}});
-    CHECK(Tree{1} < Tree{std::vector{Tree{2}}});
-    CHECK(!(Tree{std::vector{Tree{2}}} < Tree{1}));
-    CHECK(Tree{std::vector<Tree>{}} < Tree{std::vector{Tree{2}}});
-    CHECK(Tree{std::vector<Tree>{}} < Tree{std::vector{Tree{2}}});
+    CHECK(Tree{Trees{Tree{1}}} < Tree{Trees{Tree{2}}});
+    CHECK(Tree{1} < Tree{Trees{Tree{2}}});
+    CHECK(!(Tree{Trees{Tree{2}}} < Tree{1}));
+    CHECK(Tree{Trees{}} < Tree{Trees{Tree{2}}});
+    CHECK(Tree{Trees{}} < Tree{Trees{Tree{2}}});
   }
   TEST_CASE("documented example") {
     std::istringstream in {
@@ -154,7 +161,7 @@ TEST_SUITE("2022-13 examples") {
       "[1,[2,[3,[4,[5,6,7]]]],8,9]\n"
       "[1,[2,[3,[4,[5,6,0]]]],8,9]\n"
     };
-    auto input = Parse(in);
+    auto const input = Parse(in);
     CHECK(13 == Part1(input));
     CHECK(140 == Part2(input));
   }

2022/CMakeLists.txt

@@ -29,7 +29,7 @@ add_executable(2022_12 12.cpp)
 target_link_libraries(2022_12 aocpp)
 
 add_executable(2022_13 13.cpp)
-target_link_libraries(2022_13 aocpp)
+target_link_libraries(2022_13 aocpp Boost::headers)
 
 add_executable(2022_16 16.cpp)
 target_link_libraries(2022_16 aocpp Boost::headers)