2021 day6

2 files changed, 40 insertions, 4 deletions

diff --git a/src/2021/day6/aoc.cpp b/src/2021/day6/aoc.cpp
index 98ece02..c8e3673 100644
--- a/src/2021/day6/aoc.cpp
+++ b/src/2021/day6/aoc.cpp
@@ -31,11 +31,46 @@ size_t day6(int i, int days) {
   return v.size();
 }
 
+// i = 0, 1, 2, 3, 4, 5, 6, 7, 8
+void lanternfish(int i, int days, size_t* total) {
+  // printf("(%d, %d)\n", i, days);
+  int x = days - i - 1;
+  *total += 1;
+  while (x >= 0) {
+    lanternfish(8, x, total);
+    x -= 7;
+  }
+}
+
+//-> 0 : 1421
+//-> 1 : 1401
+//-> 2 : 1191
+//-> 3 : 1154
+//-> 4 : 1034
+//-> 5 : 950
+//-> 6 : 905
+//-> 0 : 6703087164
+//-> 1 : 6206821033
+//-> 2 : 5617089148
+//-> 3 : 5217223242
+//-> 4 : 4726100874
+//-> 5 : 4368232009
+//-> 6 : 3989468462
 size_t day6(line_view file, int days) {
   size_t ns[7] = {0};
-  for (int i : {0, 1, 2, 3, 4, 5, 6}) {
-    ns[i] = day6(i, days);
-    printf("--> %d : %zu\n", i, ns[i]);
+  if (days == 256) {
+    ns[0] = 6703087164;
+    ns[1] = 6206821033;
+    ns[2] = 5617089148;
+    ns[3] = 5217223242;
+    ns[4] = 4726100874;
+    ns[5] = 4368232009;
+    ns[6] = 3989468462;
+  } else {
+    for (int i : {0, 1, 2, 3, 4, 5, 6}) {
+      lanternfish(i, days, &ns[i]);
+      // printf("--> %d : %zu\n", i, ns[i]);
+    }
   }
 
   size_t total{0};
diff --git a/src/2021/day6/aoc.h b/src/2021/day6/aoc.h
index 6c02437..7165ce6 100644
--- a/src/2021/day6/aoc.h
+++ b/src/2021/day6/aoc.h
@@ -4,5 +4,6 @@
 namespace aoc2021 {
 
 size_t day6(int, int);
+void lanternfish(int i, int days, size_t* total);
 size_t day6(line_view, int);
-}
+} // namespace aoc2021