aoc 2025, day 12, quick and dirty solution.. :/HEADmaster

1 files changed, 92 insertions, 0 deletions

diff --git a/2025/src/day12.cpp b/2025/src/day12.cpp
new file mode 100644
index 0000000..d6f9277
--- /dev/null
+++ b/2025/src/day12.cpp
@@ -0,0 +1,92 @@
+#include <array>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+using Region = tuple<long, long, array<long, 6>>;
+
+tuple<map<long, long>, vector<Region>>
+read_file(const filesystem::path& filename)
+{
+        ifstream       file{ filename };
+        vector<string> lines;
+
+        for ( string line; getline(file, line); ) {
+                lines.emplace_back(line);
+        }
+
+        map<long, long> areas;
+
+        size_t idx = 0;
+        for ( ;; idx += 5 ) {
+                if ( lines.at(idx).at(1) != ':' ) {
+                        break;
+                }
+
+                const long num = lines.at(idx).at(0) - '0';
+
+                long count = 0;
+                for ( size_t j = idx + 1; j != idx + 4; ++j ) {
+                        count += ranges::count(lines.at(j), '#');
+                }
+
+                areas[num] = count;
+        }
+
+        vector<Region> regions;
+        for ( ; idx != lines.size(); ++idx ) {
+                static const regex rgx(R"(^(\d+)x(\d+):\s+(\d+)\s+(\d+)\s+(\d+)\s+(\d+)\s+(\d+)\s+(\d+)$)");
+
+                smatch match;
+                if ( !regex_match(lines.at(idx), match, rgx) ) {
+                        continue;
+                }
+
+                regions.emplace_back(
+                    stol(match[1]), // width
+                    stol(match[2]), // height
+                    array<long, 6>{
+                        stol(match[3]),
+                        stol(match[4]),
+                        stol(match[5]),
+                        stol(match[6]),
+                        stol(match[7]),
+                        stol(match[8]) } // counts
+                );
+        }
+
+        return { areas, regions };
+}
+
+void
+part1(const map<long, long>& areas, const vector<Region>& regions)
+{
+        const auto result = ranges::count_if(regions, [&](const auto& region) {
+                const auto& [width, height, counts] = region;
+
+                long required = 0;
+                for ( size_t i = 0; i != counts.size(); ++i ) {
+                        required += counts.at(i) * areas.at(static_cast<long>(i));
+                }
+                return required < width * height;
+        });
+
+        cout << "Part 1: " << result << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        const auto [areas, regions] = read_file("data/day12.txt");
+        part1(areas, regions);
+}