1 files changed, 56 insertions, 0 deletions

diff --git a/2025/src/day09.cpp b/2025/src/day09.cpp
new file mode 100644
index 0000000..f46112a
--- /dev/null
+++ b/2025/src/day09.cpp
@@ -0,0 +1,56 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+using Pos = tuple<long, long>;
+
+vector<Pos>
+read_file(const filesystem::path& filename)
+{
+        ifstream file{ filename };
+
+        vector<Pos> data;
+
+        long x{};
+        long y{};
+        char skip{};
+
+        while ( file >> x >> skip >> y ) {
+                data.emplace_back(x, y);
+        }
+        return data;
+}
+
+void
+part1(const vector<Pos>& data)
+{
+        auto area = numeric_limits<long>::min();
+
+        for ( size_t i = 0; i != data.size(); ++i ) {
+                for ( size_t j = i + 1; j != data.size(); ++j ) {
+                        const auto [x1, y1] = data[i];
+                        const auto [x2, y2] = data[j];
+
+                        const auto width  = abs(x1 - x2) + 1;
+                        const auto height = abs(y1 - y2) + 1;
+
+                        area = max(area, width * height);
+                }
+        }
+        cout << "Part 1: " << area << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        auto data = read_file("data/day09.txt");
+        part1(data);
+}