Solutions for 2018 day 7

2018/puzzle-07-01.cc

@@ -0,0 +1,68 @@
+//
+// Created by Matthew Gretton-Dann on 01/12/2022.
+//
+
+#include <algorithm>
+#include <cstdlib>
+#include <iomanip>
+#include <iostream>
+#include <map>
+#include <numeric>
+#include <regex>
+#include <utility>
+
+struct Step
+{
+  explicit Step(std::string const& dependencies) : done_(false), dependencies_(dependencies) {}
+
+  bool done_;
+  std::string dependencies_;
+};
+
+using UInt = std::int64_t;
+using StepMap = std::map<char, Step>;
+
+auto main() -> int
+{
+  std::string line;
+  StepMap step_map;
+  std::regex const re{"Step ([A-Z]) must be finished before step ([A-Z]) can begin."};
+
+  // Read data
+  while (std::getline(std::cin, line)) {
+    std::smatch m;
+    if (!std::regex_match(line, m, re)) {
+      std::cerr << "Unable to interpret: " << line << "\n";
+      return EXIT_FAILURE;
+    }
+    char id{m.str(2)[0]};
+    auto [it, success] = step_map.insert({id, Step(m.str(1))});
+    if (!success) {
+      it->second.dependencies_ += m.str(1);
+    }
+
+    // Ensure we have every id we've seen present in the map even if it has no dependencies
+    step_map.insert({m.str(1)[0], Step("")});
+  }
+
+  std::string order;
+  while (!std::all_of(step_map.begin(), step_map.end(),
+                      [](auto const& step) { return step.second.done_; })) {
+    char to_do{'Z' + 1};
+    for (auto& step : step_map) {
+      if (step.second.done_) {
+        continue;
+      }
+      auto const& dependencies{step.second.dependencies_};
+      if (std::all_of(dependencies.begin(), dependencies.end(),
+                      [&step_map](auto c) { return step_map.find(c)->second.done_; })) {
+        to_do = std::min(step.first, to_do);
+      }
+    }
+    order += to_do;
+    step_map.find(to_do)->second.done_ = true;
+  }
+
+  std::cout << "Order: " << order << "\n";
+  return EXIT_SUCCESS;
+}