1 files changed, 101 insertions, 0 deletions

diff --git a/2024/src/day12.cpp b/2024/src/day12.cpp
new file mode 100644
index 0000000..6a23730
--- /dev/null
+++ b/2024/src/day12.cpp
@@ -0,0 +1,101 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <queue>
+#include <set>
+#include <string>
+#include <tuple>
+#include <vector>
+using namespace std;
+
+using pos_type = tuple<size_t, size_t>;
+
+map<pos_type, char>
+read_file(string_view filename)
+{
+        fstream             input{ filename };
+        map<pos_type, char> data;
+
+        size_t yPos = 0;
+        for ( string line; getline(input, line); ) {
+                for ( size_t xPos = 0; xPos != line.size(); ++xPos ) {
+                        data[{ xPos, yPos }] = line.at(xPos);
+                }
+                ++yPos;
+        }
+        return data;
+}
+
+constexpr vector<pos_type>
+neighbors(pos_type pos)
+{
+        const auto [x, y] = pos;
+        return { { x - 1, y }, { x, y - 1 }, { x + 1, y }, { x, y + 1 } };
+}
+
+void
+part1(const map<pos_type, char>& data)
+{
+        auto data_copy = data;
+
+        auto flood_fill = [&](pos_type start) {
+                set<pos_type>   area;
+                queue<pos_type> queue;
+                queue.push(start);
+
+                while ( !queue.empty() ) {
+                        auto pos = queue.front();
+                        queue.pop();
+
+                        if ( !data_copy.contains(pos) ) {
+                                continue;
+                        }
+
+                        auto digit = data_copy.at(pos);
+
+                        for ( const auto& neighbor: neighbors(pos) ) {
+                                if ( !data_copy.contains(neighbor) ) {
+                                        continue;
+                                }
+                                if ( data_copy.at(neighbor) != digit ) {
+                                        continue;
+                                }
+                                queue.push(neighbor);
+                        }
+
+                        area.insert(pos);
+                        data_copy.erase(pos);
+                }
+                return area;
+        };
+
+        auto count_edges = [](const set<pos_type>& area) -> size_t {
+                size_t sum = 0;
+
+                for ( const auto& pos: area ) {
+                        for ( const auto& neighbor: neighbors(pos) ) {
+                                if ( !area.contains(neighbor) ) {
+                                        ++sum;
+                                }
+                        }
+                }
+
+                return sum;
+        };
+
+        size_t sum = 0;
+        while ( !data_copy.empty() ) {
+                auto area  = flood_fill(data_copy.begin()->first);
+                auto edges = count_edges(area);
+
+                sum += area.size() * edges;
+        }
+        cout << sum << endl;
+}
+
+int
+main()
+{
+        auto data = read_file("data/day12.txt");
+        part1(data);
+}