2 files changed, 59 insertions, 6 deletions

diff --git a/src/2015/day12/aoc.cpp b/src/2015/day12/aoc.cpp
index 3b1ed2b..33db5d0 100644
--- a/src/2015/day12/aoc.cpp
+++ b/src/2015/day12/aoc.cpp
@@ -1,8 +1,9 @@
 #include "aoc.h"
+#include <stack>
 
 namespace aoc2015 {
 
-int parse_day12(const char* p1, const char* p2) {
+int get_number(const char* p1, const char* p2) {
   int sign = *(p1 - 1) == '-' ? -1 : 1;
   int d{0};
   while (p1 != p2) {
@@ -12,12 +13,12 @@ int parse_day12(const char* p1, const char* p2) {
   return sign * d;
 }
 
-int day12(line_view file) {
+int parse_day12(line_view s) {
   int total = 0;
-  const char* p1 = file.line;
+  const char* p1 = s.line;
   const char* p2 = p1;
   bool to_parse = false;
-  while (p2 < file.line + file.length) {
+  while (p2 < s.line + s.length) {
     if (*p2 >= '0' && *p2 <= '9') {
       if (!to_parse) {
         p1 = p2;
@@ -25,16 +26,67 @@ int day12(line_view file) {
       }
     } else {
       if (to_parse) {
-        total += parse_day12(p1, p2);
+        total += get_number(p1, p2);
         to_parse = !to_parse;
       }
     }
     p2++;
   }
   if (to_parse) {
-    total += parse_day12(p1, p2);
+    total += get_number(p1, p2);
   }
   return total;
 }
 
+int day12(line_view file) { return parse_day12(file); }
+
+struct day12_object {
+  const char* p1;
+
+  int fold(const char* p2) {
+    line_view lv{p1, p2};
+    const char* p = lv.contains("red");
+    return (p != nullptr) ? 0 : parse_day12(lv);
+  }
+};
+
+// {{x}   x} = 0
+// {{x} ...} = ...
+// {{...} x} = 0
+// {{...} .} = ... + .
+int day12_part2(line_view file) {
+  int total = 0;
+  std::stack<day12_object> os;
+  std::stack<int> is;
+  const char* p = file.line;
+  const char* p1 = p;
+  while (p < file.line + file.length) {
+    if (*p == '{') {
+      if (os.empty()) {
+        total += parse_day12({p1, p});
+        p1 = p;
+      }
+      os.push({p});
+    }
+    if (*p == '}') {
+      auto o = os.top();
+      is.push(o.fold(p));
+      os.pop();
+      if (os.empty()) {
+        while (!is.empty()) {
+          total += is.top();
+          is.pop();
+        }
+        p1 = p;
+      } else {
+        auto& oo = os.top();
+        oo.p1 = p;
+      }
+    }
+    p++;
+  }
+  total += parse_day12({p1, p});
+  return total;
+}
+
 } // namespace aoc2015
diff --git a/src/2015/day12/aoc.h b/src/2015/day12/aoc.h
index 66d7164..10114a6 100644
--- a/src/2015/day12/aoc.h
+++ b/src/2015/day12/aoc.h
@@ -4,5 +4,6 @@
 namespace aoc2015 {
 
 int day12(line_view file);
+int day12_part2(line_view file);
 
 }