1 files changed, 158 insertions, 0 deletions

diff --git a/2017/src/day22.cpp b/2017/src/day22.cpp
new file mode 100644
index 0000000..2567fb1
--- /dev/null
+++ b/2017/src/day22.cpp
@@ -0,0 +1,158 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <set>
+#include <string>
+#include <tuple>
+
+using namespace std;
+
+namespace {
+
+set<tuple<int, int>>
+read_file(const filesystem::path& filename)
+{
+        ifstream             file{ filename };
+        set<tuple<int, int>> data;
+
+        int row = 0;
+        for ( string line; getline(file, line); ) {
+                int col = 0;
+
+                for ( char chr: line ) {
+                        if ( chr == '#' ) {
+                                data.emplace(col, row);
+                        }
+                        ++col;
+                }
+
+                ++row;
+        }
+
+        return data;
+}
+
+#if 0
+void
+print(const set<tuple<int, int>>& grid, tuple<int, int> pos)
+{
+        for ( int y = -5; y < 5; ++y ) {
+                for ( int x = -5; x < 5; ++x ) {
+                        auto coord = make_tuple(x, y);
+
+                        if ( pos == coord ) {
+                                cout << '[';
+                        }
+                        else {
+                                cout << ' ';
+                        }
+
+                        auto chr = grid.contains(coord) ? '#' : '.';
+                        cout << chr;
+
+                        if ( pos == coord ) {
+                                cout << ']';
+                        }
+                        else {
+                                cout << ' ';
+                        }
+                }
+                cout << '\n';
+        }
+        cout << '\n';
+}
+#endif
+
+void
+part1(set<tuple<int, int>> grid, tuple<int, int> pos)
+{
+        const array<tuple<int, int>, 4> dirs{
+                make_tuple(-1, 0),
+                make_tuple(0, -1),
+                make_tuple(1, 0),
+                make_tuple(0, 1)
+        };
+        unsigned dir = 1; // up
+
+        int infections = 0;
+        for ( int i = 0; i != 10000; ++i ) {
+                if ( grid.contains(pos) ) {
+                        dir = (dir + 1) % 4;
+                        grid.erase(pos);
+                }
+                else {
+                        dir = (dir + 3) % 4;
+                        grid.insert(pos);
+                        ++infections;
+                }
+
+                auto [dx, dy] = dirs.at(dir);
+                get<0>(pos) += dx;
+                get<1>(pos) += dy;
+        }
+        cout << "Part1: " << infections << '\n';
+}
+
+void
+part2(set<tuple<int, int>> grid, tuple<int, int> pos)
+{
+        const array<tuple<int, int>, 4> dirs{
+                make_tuple(-1, 0),
+                make_tuple(0, -1),
+                make_tuple(1, 0),
+                make_tuple(0, 1)
+        };
+        unsigned dir = 1; // up
+
+        static const int weak     = 0;
+        static const int infected = 1;
+        static const int flagged  = 2;
+
+        map<tuple<int, int>, int> grid_;
+        for ( const auto& value: grid ) {
+                grid_[value] = infected;
+        }
+
+        int infections = 0;
+        for ( int i = 0; i != 10000000; ++i ) {
+                if ( !grid_.contains(pos) ) {
+                        grid_[pos] = weak;
+                        dir        = (dir + 3) % 4;
+                }
+                else {
+                        switch ( grid_[pos] ) {
+                        case weak:
+                                grid_[pos] = infected;
+                                ++infections;
+                                break;
+                        case infected:
+                                grid_[pos] = flagged;
+                                dir        = (dir + 1) % 4;
+                                break;
+                        case flagged:
+                                grid_.erase(pos);
+                                dir = (dir + 2) % 4;
+                                break;
+                        default:
+                                cerr << "Wrong state!!" << '\n';
+                                return;
+                        }
+                }
+
+                auto [dx, dy] = dirs.at(dir);
+                get<0>(pos) += dx;
+                get<1>(pos) += dy;
+        }
+        cout << "Part2: " << infections << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        auto grid = read_file("data/day22.txt");
+        part1(grid, { 12, 12 });
+        part2(grid, { 12, 12 });
+}