3 files changed, 95 insertions, 1 deletions
diff --git a/src/2020/day7/aoc.cpp b/src/2020/day7/aoc.cpp
index 2519be1..9ed0f99 100644
--- a/src/2020/day7/aoc.cpp
+++ b/src/2020/day7/aoc.cpp
@@ -1,4 +1,35 @@
 #include "aoc.h"
+#include <algorithm>
 
 namespace aoc2020 {
+
+bool find_color(color_bag* bag, line_view color) {
+  if (bag->color == color) {
+    return true;
+  } else {
+    for (auto& p : bag->bags) {
+      if (find_color(p.first, color)) {
+        return true;
+      }
+    }
+    return false;
+  }
+}
+
+int day7(line_view file, const char* color) {
+  bag_regulations rs;
+  per_line(file, [&rs](line_view lv) {
+    rs.parse(lv);
+    return true;
+  });
+
+  int total{0};
+  for (auto& b : rs.regulations) {
+    if (!(b.second->color == color)) {
+      total += int(find_color(b.second, color));
+    }
+  }
+
+  return total;
 }
+} // namespace aoc2020
diff --git a/src/2020/day7/aoc.h b/src/2020/day7/aoc.h
index 8006657..189237e 100644
--- a/src/2020/day7/aoc.h
+++ b/src/2020/day7/aoc.h
@@ -1,5 +1,59 @@
 #pragma once
 #include "common.h"
+#include <unordered_map>
+#include <vector>
 
 namespace aoc2020 {
-}
+
+struct color_bag {
+  line_view color;
+  std::vector<std::pair<color_bag*, int>> bags;
+};
+
+struct bag_regulations {
+  std::unordered_map<line_view, color_bag*> regulations;
+
+  void get_number(const char** pp, int* d) {
+    const char* p = *pp;
+    *d = 0;
+    while (*p >= '0' && *p <= '9') {
+      *d = *d * 10 + *p - '0';
+      p++;
+    }
+    *pp = p;
+  }
+
+  std::pair<color_bag*, int> get_bag(const char* p1, const char* p2) {
+    int d{0};
+    get_number(&p1, &d);
+    line_view color = {d > 0 ? p1 + 1 : p1, *(p2 - 1) == 's' ? p2 - 5 : p2 - 4};
+    color_bag* bag = nullptr;
+    auto it = regulations.find(color);
+    if (it == regulations.end()) {
+      bag = new color_bag{color, {}};
+      regulations.insert({color, bag});
+    } else {
+      bag = it->second;
+    }
+    return {bag, d};
+  }
+
+  void parse(line_view lv) {
+    const char* p1 = lv.line;
+    const char* p2 = lv.line + lv.length;
+    const char* p = lv.contains("contain");
+    auto pa1 = get_bag(p1, p - 1);
+    p1 = p + 8;
+    p = p1;
+    while (p < p2) {
+      if (*p == ',' || *p == '.') {
+        pa1.first->bags.push_back(get_bag(p1, p));
+        p1 = p + 2;
+      }
+      p++;
+    }
+  }
+};
+
+int day7(line_view, const char*);
+} // namespace aoc2020
diff --git a/src/2020/day7/input0 b/src/2020/day7/input0
new file mode 100644
index 0000000..1cec74f
--- /dev/null
+++ b/src/2020/day7/input0
@@ -0,0 +1,9 @@
+light red bags contain 1 bright white bag, 2 muted yellow bags.
+dark orange bags contain 3 bright white bags, 4 muted yellow bags.
+bright white bags contain 1 shiny gold bag.
+muted yellow bags contain 2 shiny gold bags, 9 faded blue bags.
+shiny gold bags contain 1 dark olive bag, 2 vibrant plum bags.
+dark olive bags contain 3 faded blue bags, 4 dotted black bags.
+vibrant plum bags contain 5 faded blue bags, 6 dotted black bags.
+faded blue bags contain no other bags.
+dotted black bags contain no other bags.