1 files changed, 89 insertions, 1 deletions
diff --git a/src/2017/day22/aoc.cpp b/src/2017/day22/aoc.cpp
index b2e2dfb..3e9a907 100644
--- a/src/2017/day22/aoc.cpp
+++ b/src/2017/day22/aoc.cpp
@@ -1,6 +1,94 @@
 #include "aoc.h"
+#include <set>
 
 namespace aoc2017 {
 
-std::pair<int64_t, int64_t> day22(line_view) { return {0, 0}; }
+static int radias = 12; // demo 25/2 = 12 input
+enum facing {
+  f_up,
+  f_down,
+  f_right,
+  f_left,
+};
+
+struct vpos {
+  int x;
+  int y;
+  facing f;
+};
+
+static vpos turn_right(vpos p) {
+  facing fs[4] = {f_right, f_left, f_down, f_up};
+  return {p.x, p.y, fs[(int)p.f]};
+}
+
+static vpos turn_left(vpos p) {
+  facing fs[4] = {f_left, f_right, f_up, f_down};
+  return {p.x, p.y, fs[(int)p.f]};
+}
+
+static vpos move(vpos p) {
+  vpos vs[4] = {
+      {p.x, p.y - 1, p.f},
+      {p.x, p.y + 1, p.f},
+      {p.x + 1, p.y, p.f},
+      {p.x - 1, p.y, p.f},
+  };
+  return vs[(int)p.f];
+}
+
+vpos burst(std::set<node22>& infected, vpos p, int* c) {
+  auto it = infected.find({p.x, p.y});
+  bool is_infected = it != infected.end();
+  // If the current node is infected, it turns to its right. Otherwise, it turns to its left. (Turning is done in-place;
+  // the current node does not change.)
+  vpos px = is_infected ? turn_right(p) : turn_left(p);
+
+  // If the current node is clean, it becomes infected. Otherwise, it becomes
+  // cleaned. (This is done after the node is considered for the purposes of changing direction.) The virus carrier
+  if (!is_infected) {
+    infected.insert({p.x, p.y});
+    *c += 1;
+  } else {
+    infected.erase(it);
+  }
+
+  // moves forward one node in the direction it is facing.
+  px = move(px);
+  return px;
+}
+
+static void load(std::set<node22>& is, int r, line_view lv) {
+  const char* p = lv.line;
+  int x = 0;
+  while (*(p + x) != '\n') {
+    if (*(p + x) == '#') {
+      node22 n{x - radias, r - radias};
+      is.insert(n);
+    }
+    x++;
+  }
+}
+
+std::pair<int64_t, int64_t> day22(line_view file) {
+  std::set<node22> infected;
+
+  int r{0};
+  per_line(file, [&r, &infected](line_view lv) {
+    load(infected, r++, lv);
+    return true;
+  });
+
+  vpos p{0, 0, f_up};
+  int t0{0};
+  for (int i = 0; i < 10000; i++) {
+    p = burst(infected, p, &t0);
+  }
+
+  // for (auto& n : infected) {
+  //   printf("%d,%d\n", n.x, n.y);
+  // }
+  return {t0, 0};
+}
+
 } // namespace aoc2017