1 files changed, 116 insertions, 0 deletions

diff --git a/2022/src/day09.cpp b/2022/src/day09.cpp
new file mode 100644
index 0000000..8b99942
--- /dev/null
+++ b/2022/src/day09.cpp
@@ -0,0 +1,116 @@
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <set>
+#include <vector>
+using namespace std;
+
+vector<tuple<char, int>>
+read_file(string_view filename)
+{
+        fstream                  input{ filename };
+        vector<tuple<char, int>> result;
+
+        char dir   = 0;
+        int  count = 0;
+
+        while ( input >> dir >> count ) {
+                result.emplace_back(dir, count);
+        }
+
+        return result;
+}
+
+int
+distance(const tuple<int, int>& head, const tuple<int, int>& tail)
+{
+        auto dist_x = abs(get<0>(head) - get<0>(tail));
+        auto dist_y = abs(get<1>(head) - get<1>(tail));
+        return max(dist_x, dist_y);
+};
+
+static map<char, tuple<int, int>> direction = {
+        { 'R', { +1, 0 } },
+        { 'L', { -1, 0 } },
+        { 'U', { 0, +1 } },
+        { 'D', { 0, -1 } }
+};
+
+void
+part1(const vector<tuple<char, int>>& data)
+{
+        tuple<int, int> head = { 0, 0 };
+        tuple<int, int> tail = head;
+
+        set<tuple<int, int>> positions;
+
+        for ( auto [dir, count]: data ) {
+                while ( count-- > 0 ) {
+                        const auto [delta_x, delta_y] = direction[dir];
+                        const auto old_head           = head;
+
+                        get<0>(head) += delta_x;
+                        get<1>(head) += delta_y;
+
+                        if ( distance(head, tail) > 1 ) {
+                                tail = old_head;
+                        }
+
+                        positions.insert(tail);
+                }
+        }
+
+        cout << positions.size() << endl;
+}
+
+void
+part2(const vector<tuple<char, int>>& data)
+{
+        static const auto rope_size = 10;
+
+        array<tuple<int, int>, rope_size> rope;
+
+        set<tuple<int, int>> positions;
+
+        for ( auto [dir, count]: data ) {
+                while ( count-- > 0 ) {
+                        auto [delta_x, delta_y] = direction[dir];
+
+                        get<0>(rope[0]) += delta_x;
+                        get<1>(rope[0]) += delta_y;
+
+                        for ( size_t i = 1; i < rope.size(); ++i ) {
+                                auto& head = rope.at(i - 1);
+                                auto& tail = rope.at(i);
+
+                                if ( distance(head, tail) > 1 ) {
+                                        delta_x = get<0>(head) - get<0>(tail);
+                                        delta_y = get<1>(head) - get<1>(tail);
+
+                                        if ( abs(delta_x) > 1 ) {
+                                                delta_x /= abs(delta_x);
+                                        }
+                                        if ( abs(delta_y) > 1 ) {
+                                                delta_y /= abs(delta_y);
+                                        }
+
+                                        get<0>(tail) += delta_x;
+                                        get<1>(tail) += delta_y;
+                                }
+                        }
+
+                        positions.insert(rope[9]);
+                }
+        }
+
+        cout << positions.size() << endl;
+}
+
+int
+main()
+{
+        const auto data = read_file("data/day09.txt");
+        part1(data);
+        part2(data);
+}