ideas for day 21 part 2

1 files changed, 7 insertions, 0 deletions

diff --git a/2023/src/bin/day_21.rs b/2023/src/bin/day_21.rs
index d5126bd..11cdc07 100644
--- a/2023/src/bin/day_21.rs
+++ b/2023/src/bin/day_21.rs
@@ -16,6 +16,13 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     dbg!(&walled_garden.count_walkable());
 
     let mut open_garden = OpenGarden::parser(&input).unwrap().1;
+    // - the paths straight up / down, and left / right from the middle and edges are clear.
+    // - this would allow finding a "single tile" version (eg part 1) to see how much of a tile could be filled at the boundaries.
+    // - start at the top boundary I can get into, 26501365 / 131
+    // - when I find a fully explored garden, I can extrapolate that any closer gardens are also filled out
+    // - for filled out gardens, there will be an 'even' and an 'odd' answer (alternating checkerboard). choose the right one to add it.
+    // - this is still around 202300 pages in each direction, so multiplying the rows etc seems like a good idea. Eg do the two sides, then multiply out the fully explored middle.
+
     let open_iters = 26501365;
     for i in 0..open_iters {
         if i % 100000 == 0 {