1 files changed, 67 insertions, 1 deletions
diff --git a/src/2017/day12/aoc.cpp b/src/2017/day12/aoc.cpp
index 30f0501..0323e71 100644
--- a/src/2017/day12/aoc.cpp
+++ b/src/2017/day12/aoc.cpp
@@ -2,5 +2,71 @@
 
 namespace aoc2017 {
 
-std::pair<int64_t, int64_t> day12(line_view) { return {0, 0}; }
+static void get_number(const char** pp, int* d) {
+  const char* p = *pp;
+  while (*p >= '0' && *p <= '9') {
+    *d = *d * 10 + *p - '0';
+    p++;
+  }
+  *pp = p;
+}
+
+struct record12 {
+  int ns[10] = {0};
+  bool connected = false;
+
+  void print() const noexcept {
+    for (auto n : ns) {
+      printf("%d ", n);
+    }
+    printf("\n");
+  }
+
+  record12(line_view lv) {
+    const char* p = lv.line;
+    int i{0};
+    while (p < lv.line + lv.length) {
+      if (*p >= '0' && *p <= '9') {
+        get_number(&p, &ns[i++]);
+      }
+      p++;
+    }
+  }
+};
+
+void mark_connected(size_t i, std::vector<record12>& rs, int* total) {
+  auto& r = rs[i];
+  if (!r.connected) {
+    *total += 1;
+    r.connected = true;
+    for (int x = 1; x < 10; x++) {
+      if (r.ns[x] > 0) {
+        mark_connected(r.ns[x], rs, total);
+      }
+    }
+  }
+}
+
+std::pair<int64_t, int64_t> day12(line_view file) {
+  std::vector<record12> rs;
+  per_line(file, [&rs](line_view lv) {
+    rs.emplace_back(lv);
+    return true;
+  });
+
+  int total{0};
+  mark_connected(0, rs, &total);
+  int t0 = total;
+  int t1 = 1;
+
+  for (size_t i = 1; i < rs.size() && total < (int)rs.size(); i++) {
+    int tx = total;
+    mark_connected(i, rs, &total);
+    if (total > tx) {
+      t1 += 1;
+    }
+  }
+
+  return {t0, t1};
+}
 } // namespace aoc2017