2023 Day 4 Part 2

2023/puzzle-04-02.cc

@@ -0,0 +1,86 @@
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <iterator>
+#include <map>
+#include <numeric>
+#include <string>
+#include <vector>
+
+using UInt = std::uint64_t;
+using NumVec = std::vector<UInt>;
+
+struct Card {
+    explicit Card(std::string line) {
+      assert(line.substr(0, 4) == "Card");
+      line = line.substr(4);
+
+      /* Get the ID. */
+      std::size_t pos{0};
+      id_ = std::stoull(line, &pos);
+      assert(line[pos] == ':');
+      line = line.substr(pos + 1);
+
+      /* Read in the winners. */
+      while (line[0] != '|') {
+        winners_.push_back(std::stoull(line, &pos));
+        while (line[pos] == ' ') { ++pos; }
+        line = line.substr(pos);
+      }
+      std::sort(winners_.begin(), winners_.end());
+
+      /* Read in the numbers we have. */
+      line = line.substr(1);
+      while (!line.empty()) {
+        got_.push_back(std::stoull(line, &pos));
+        line = line.substr(pos);
+      }
+      std::sort(got_.begin(), got_.end());
+    }
+
+    [[nodiscard]] auto operator<(Card const &rhs) const -> bool {
+      return id_ < rhs.id_;
+    }
+
+    [[nodiscard]] auto match_count() const -> UInt {
+      NumVec intersection;
+      std::set_intersection(winners_.begin(), winners_.end(), got_.begin(), got_.end(),
+                            std::back_inserter(intersection));
+      return intersection.size();
+    }
+
+    UInt id_{0};
+    NumVec got_;
+    NumVec winners_;
+};
+
+using CardMap = std::map<Card, UInt>;
+
+auto main() -> int try {
+  std::string line;
+  CardMap cards;
+  while (std::getline(std::cin, line)) {
+    Card card(line);
+    cards.insert({card, 1});
+  }
+
+  for (auto it{cards.begin()}; it != cards.end(); ++it) {
+    auto matched = it->first.match_count();
+    auto it2 = it;
+    while (matched-- != 0) {
+      ++it2;
+      it2->second += it->second;
+    }
+  }
+
+  auto count = std::accumulate(cards.begin(), cards.end(), UInt{0},
+                               [](UInt a, auto const &it) { return a + it.second; });
+  std::cout << "Final count of cards: " << count << '\n';
+  return EXIT_SUCCESS;
+}
+catch (...) {
+  std::cerr << "Uncaught exception.\n";
+  return EXIT_FAILURE;
+}