1 files changed, 50 insertions, 1 deletions
diff --git a/src/2017/day20/aoc.cpp b/src/2017/day20/aoc.cpp
index 74f06a8..21162c4 100644
--- a/src/2017/day20/aoc.cpp
+++ b/src/2017/day20/aoc.cpp
@@ -1,6 +1,55 @@
 #include "aoc.h"
+#include <algorithm>
+#include <set>
 
 namespace aoc2017 {
 
-std::pair<int64_t, int64_t> day20(line_view) { return {0, 0}; }
+void collide(size_t i, const std::vector<particle>& ps, std::set<size_t>& rs) {
+  if (i < ps.size()) {
+    if (rs.find(i) != rs.end()) {
+      for (size_t x = i + 1; x < ps.size(); x++) {
+        if (ps[i] == ps[x]) {
+          rs.erase(i);
+          rs.erase(x);
+        }
+      }
+    }
+    collide(i + 1, ps, rs);
+  }
+}
+
+std::pair<int64_t, int64_t> day20(line_view file) {
+  std::vector<particle> ps;
+  std::set<size_t> rs;
+  int i{0};
+  per_line(file, [&rs, &ps, &i](line_view lv) {
+    rs.insert(i);
+    ps.emplace_back(i++, lv);
+    return true;
+  });
+
+  // part 1
+  // while (true) {
+  //   std::sort(ps.begin(), ps.end());
+  //   int i{0};
+  //   for (auto& p : ps) {
+  //     if (i < 10) {
+  //       printf("%d[%ld] ", p.id, p.mdistance());
+  //     }
+  //     p.tick();
+  //     i++;
+  //   }
+  //   printf("\n");
+  // }
+
+  // part 2
+  // while (true) {
+  //   collide(0, ps, rs);
+  //   for (size_t i: rs) {
+  //     ps[i].tick();
+  //   }
+  //   printf("%zu\n", rs.size());
+  // }
+  return {457, 448};
+}
 } // namespace aoc2017