2 files changed, 52 insertions, 6 deletions

diff --git a/src/2020/day6/aoc.cpp b/src/2020/day6/aoc.cpp
index d64262e..5f44585 100644
--- a/src/2020/day6/aoc.cpp
+++ b/src/2020/day6/aoc.cpp
@@ -4,23 +4,27 @@
 
 namespace aoc2020 {
 
-int day6(line_view file) {
+std::pair<int, int> day6(line_view file) {
   std::vector<question_group> gs;
 
   const char* p1 = file.line;
   const char* p = p1;
   while (p < file.line + file.length) {
     if (*p == '\n' && *(p + 1) == '\n') {
-      gs.emplace_back(line_view{p1, p});
+      gs.emplace_back(line_view{p1, p + 1});
       p1 = p + 2;
     }
     p++;
   }
   gs.emplace_back(line_view{p1, p});
 
-  int total{0};
-  std::for_each(gs.begin(), gs.end(), [&total](const question_group& g) { total += g.summary(); });
-  return total;
+  int t0{0};
+  int t1{0};
+  std::for_each(gs.begin(), gs.end(), [&t0, &t1](const question_group& g) {
+    t0 += g.summary();
+    t1 += g.common();
+  });
+  return {t0, t1};
 }
 
 } // namespace aoc2020
diff --git a/src/2020/day6/aoc.h b/src/2020/day6/aoc.h
index dc2989d..5f5b2b6 100644
--- a/src/2020/day6/aoc.h
+++ b/src/2020/day6/aoc.h
@@ -1,5 +1,6 @@
 #pragma once
 #include "common.h"
+#include <vector>
 
 namespace aoc2020 {
 
@@ -15,6 +16,47 @@ struct question_group {
     return total;
   }
 
+  int common(const std::vector<line_view>& vs) const noexcept {
+    line_view shortest{nullptr, INT32_MAX};
+    for (auto& l : vs) {
+      if (l.length < shortest.length) {
+        shortest = l;
+      }
+    }
+
+    std::vector<int> ts(shortest.length, 0);
+    int i{0};
+    per_char(shortest, [&vs, &ts, &i](char c) {
+      char t[2] = {c, '\0'};
+      for (auto& l : vs) {
+        const char* p = l.contains(line_view{t, 1});
+        ts[i] += int(p != nullptr);
+      }
+      i++;
+      return true;
+    });
+
+    int total{0};
+    for (auto i : ts) {
+      total += int(!(size_t(i) < vs.size()));
+    }
+    return total;
+  }
+
+  int common() const noexcept {
+    std::vector<line_view> ls;
+    const char* p1 = people.line;
+    const char* p = p1;
+    while (p < people.line + people.length) {
+      if (*p == '\n') {
+        ls.emplace_back(p1, p);
+        p1 = p + 1;
+      }
+      p++;
+    }
+    return common(ls);
+  }
+
   question_group(line_view lv) : people(lv) {
     const char* p = lv.line;
     while (p < lv.line + lv.length) {
@@ -26,6 +68,6 @@ struct question_group {
   }
 };
 
-int day6(line_view);
+std::pair<int, int> day6(line_view);
 
 } // namespace aoc2020