From 3300d3c35d2e228ea3774737c8cf551e6a18116f Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Mon, 4 Dec 2023 09:25:16 +0000
Subject: [PATCH] 2023 Day 4 Part 1

---
 2023/puzzle-04-01.cc | 67 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100644 2023/puzzle-04-01.cc

diff --git a/2023/puzzle-04-01.cc b/2023/puzzle-04-01.cc
new file mode 100644
index 0000000..3f14040
--- /dev/null
+++ b/2023/puzzle-04-01.cc
@@ -0,0 +1,67 @@
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <iterator>
+#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 score() const -> UInt {
+        NumVec intersection;
+        std::set_intersection(winners_.begin(), winners_.end(), got_.begin(), got_.end(),
+                              std::back_inserter(intersection));
+        return intersection.empty() ? 0 : (1 << (intersection.size() - 1));
+    }
+
+    UInt id_{0};
+    NumVec got_;
+    NumVec winners_;
+};
+
+auto main() -> int try {
+    std::string line;
+    UInt total_score{0};
+    while (std::getline(std::cin, line)) {
+        Card card(line);
+        total_score += card.score();
+    }
+
+    std::cout << "Score: " << total_score << '\n';
+    return EXIT_SUCCESS;
+}
+catch (...) {
+    std::cerr << "Uncaught exception.\n";
+    return EXIT_FAILURE;
+}