1 files changed, 70 insertions, 1 deletions
diff --git a/src/2017/day19/aoc.cpp b/src/2017/day19/aoc.cpp
index 8056eb8..9336fdb 100644
--- a/src/2017/day19/aoc.cpp
+++ b/src/2017/day19/aoc.cpp
@@ -2,5 +2,74 @@
 
 namespace aoc2017 {
 
-std::pair<int64_t, int64_t> day19(line_view) { return {0, 0}; }
+enum class direction {
+  up,
+  right,
+  down,
+  left,
+};
+
+struct heading {
+  pos p;
+  direction d;
+};
+
+static heading next(heading h) {
+  switch (h.d) {
+  case direction::up:
+    return {{h.p.x, h.p.y - 1}, h.d};
+  case direction::right:
+    return {{h.p.x + 1, h.p.y}, h.d};
+  case direction::down:
+    return {{h.p.x, h.p.y + 1}, h.d};
+  case direction::left:
+    return {{h.p.x - 1, h.p.y}, h.d};
+  }
+  return h;
+}
+
+// + or A-Z
+static heading next(heading h, alpha_grid& g) {
+  char c = g.get(h.p);
+  if (c == '+' || (c >= 'A' && c <= 'Z')) {
+    heading l = {{h.p.x - 1, h.p.y}, direction::left};
+    heading r = {{h.p.x + 1, h.p.y}, direction::right};
+    heading u = {{h.p.x, h.p.y - 1}, direction::up};
+    heading d = {{h.p.x, h.p.y + 1}, direction::down};
+    heading hs[4][3] = {{l, r, u}, {u, d, r}, {l, r, d}, {u, d, l}};
+    for (auto hx : hs[(int)h.d]) {
+      if (g.get(hx.p) != ' ') {
+        return hx;
+      }
+    }
+  }
+  return next(h);
+}
+
+static void move(heading h, alpha_grid& g, std::string& alpha) {
+  while (true) {
+    char c = g.get(h.p);
+    if (c == ' ')
+      break;
+    if (c >= 'A' && c <= 'Z') {
+      alpha.push_back(c);
+    }
+    h = next(h, g);
+  }
+}
+
+std::pair<std::string, int64_t> day19(line_view file) {
+  alpha_grid g{200, 200}; // input
+  // alpha_grid g{15, 6}; // demo
+  int r{0};
+  per_line(file, [&g, &r](line_view lv) {
+    g.load(r++, lv);
+    return true;
+  });
+
+  heading start = {g.start, direction::down};
+  std::string alpha{""};
+  move(start, g, alpha);
+  return {alpha, 0};
+}
 } // namespace aoc2017