1 files changed, 60 insertions, 1 deletions
diff --git a/src/2016/day19/aoc.cpp b/src/2016/day19/aoc.cpp
index bef17b4..a4b9d32 100644
--- a/src/2016/day19/aoc.cpp
+++ b/src/2016/day19/aoc.cpp
@@ -2,5 +2,64 @@
 
 namespace aoc2016 {
 
-std::pair<int64_t, int64_t> day19(line_view) { return {0, 0}; }
+struct elf {
+  int i;
+  elf* next;
+};
+
+void add_elf(elf* e1, elf* ex, elf** last) {
+  ex->next = e1;
+  (*last)->next = ex;
+  *last = ex;
+}
+
+elf* del_elf(elf* e1) {
+  elf* e = e1;
+  while (e->next != e) {
+    elf* n = e->next->next;
+    e->next = n;
+    e = n;
+  }
+  return e;
+}
+
+elf* make_elf(int n) {
+  elf* e1 = new elf;
+  e1->i = 1;
+  e1->next = e1;
+  elf* last = e1;
+  for (int i = 2; i <= n; i++) {
+    elf* e = new elf;
+    e->i = i;
+    add_elf(e1, e, &last);
+  }
+  return e1;
+}
+
+size_t last_elf(size_t n) {
+  size_t x{0};
+  size_t i{1};
+  while (x < n) {
+    x += i;
+    i <<= 1;
+  }
+  x -= (i >> 1);
+  x += 1;
+  size_t a{1};
+  while (x != n) {
+    a += 2;
+    x += 1;
+  }
+  return a;
+}
+
+std::pair<int64_t, int64_t> day19(line_view) {
+  // for (int i = 1; i < 100; i++) {
+  //   elf* e = make_elf(i);
+  //   elf* x = del_elf(e);
+  //   printf("%d\n", x->i);
+  // }
+  return {last_elf(3005290), 0};
+}
+
 } // namespace aoc2016