Initial commit

2020/puzzle-19-02.cc

@@ -0,0 +1,116 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <list>
+#include <map>
+#include <regex>
+#include <set>
+#include <string>
+#include <tuple>
+
+struct Matcher {
+  void add_rule(std::string const &s) {
+    std::size_t len = 0;
+    unsigned long id = std::stoul(s, &len);
+    assert(s[len] == ':');
+    ++len;
+    while (s[len] == ' ') {
+      ++len;
+    }
+    if (rules_.size() <= id) {
+      rules_.resize(id + 1);
+    }
+    rules_[id] = s.substr(len);
+  }
+
+  void calculate_regex() {
+    re42_ = expand_rule(42);
+    re31_ = expand_rule(31);
+  }
+
+  bool does_match(std::string const &s) const {
+    std::smatch m;
+    std::string begin = "^" + re42_ + re42_;
+    unsigned repeats = 1;
+    while (std::regex_search(s, m, std::regex(begin))) {
+      std::string end = re31_ + "$";
+      std::string suffix = m.suffix();
+      for (unsigned i = 0; i < repeats; ++i) {
+        if (std::regex_search(suffix, std::regex("^" + end))) {
+          return true;
+        }
+        end = re31_ + end;
+      }
+      begin += re42_;
+      ++repeats;
+    }
+
+    return false;
+  }
+
+private:
+  std::string expand_rule(std::size_t id) {
+    std::string re;
+    std::string const &rule = rules_[id];
+    std::size_t pos = 0;
+    bool needs_brackets = false;
+    while (pos < rule.size()) {
+      if (rule[pos] == ' ') {
+        ++pos;
+      } else if (rule[pos] == '|') {
+        re += "|";
+        needs_brackets = true;
+        ++pos;
+      } else if (rule[pos] == '"') {
+        ++pos;
+        while (pos < rule.size() && rule[pos] != '"') {
+          re += rule[pos];
+          ++pos;
+        }
+        assert(pos < rule.size());
+        assert(rule[pos] == '"');
+        ++pos;
+      } else if (std::isdigit(rule[pos])) {
+        std::size_t len = 0;
+        std::size_t subid = std::stoul(rule.substr(pos), &len);
+        pos += len;
+        re += expand_rule(subid);
+      } else {
+        assert(false);
+      }
+    }
+
+    if (needs_brackets) {
+      re = "(" + re + ")";
+    }
+    std::cout << "Rule " << id << " expands to: " << re << "\n";
+    return re;
+  }
+
+  std::vector<std::string> rules_;
+  std::string re42_;
+  std::string re31_;
+};
+
+int main(void) {
+  std::string line;
+  Matcher matcher;
+  bool adding_rules = true;
+  unsigned matches = 0;
+  while (std::getline(std::cin, line)) {
+    if (line.empty()) {
+      adding_rules = false;
+      matcher.calculate_regex();
+    } else if (adding_rules) {
+      matcher.add_rule(line);
+    } else {
+      bool m = matcher.does_match(line);
+      std::cout << line << ": does " << (m ? "" : "not ") << "match\n";
+      matches += m;
+    }
+  }
+
+  std::cout << "Total number of matches: " << matches << "\n";
+  return 0;
+}