From 4bc781585148385762d17b5f3e3ba027f7eab061 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Mon, 16 Dec 2024 13:57:13 +0000
Subject: [PATCH] 6x speed up on 24 day 16 part 2

We filter out already visited states when adding them to the work list.

We also don't sort the work list as we're already generating it in a
sorted (by cost) order.
---
 bin/day2416.ml | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/bin/day2416.ml b/bin/day2416.ml
index d9c14b6..2e6f7b7 100644
--- a/bin/day2416.ml
+++ b/bin/day2416.ml
@@ -15,10 +15,7 @@ let rec dijkstra visit check_end states =
   | (cost, state) :: t ->
       if check_end state then Some (cost, state, t)
       else
-        let new_states =
-          visit cost state |> List.sort compare_costs
-          |> List.merge compare_costs t
-        in
+        let new_states = visit cost state |> List.merge compare_costs t in
         dijkstra visit check_end new_states
 
 let visited_idx grid ((dx, dy), p) =
@@ -45,21 +42,23 @@ let visit grid visited_grid cost state =
       (cost + 1000, ((dy, -dx), p) :: state);
     ])
 
-let visit_max grid visited_grid max_cost cost state =
-  let has_visited = visited_grid.(visited_idx grid (List.hd state)) < cost in
+let has_visited grid visited_grid (cost, state) =
+  visited_grid.(visited_idx grid (List.hd state)) < cost
+
+let visit_max grid visited_grid cost state =
   let (dx, dy), ((x, y) as p) = List.hd state in
-  if has_visited then []
-  else if cost > max_cost then []
+  if has_visited grid visited_grid (cost, state) then []
   else if Aoc.Grid.get_by_pos grid p = '#' then []
   else (
-    (*Printf.printf "%d (%d, %d)\n" cost x y;
-    flush stdout;*)
+    Printf.printf "%d (%d, %d)\n" cost x y;
+    flush stdout;
     visited_grid.(visited_idx grid (List.hd state)) <- cost;
     [
       (cost + 1, ((dx, dy), (x + dx, y + dy)) :: state);
       (cost + 1000, ((-dy, dx), p) :: state);
       (cost + 1000, ((dy, -dx), p) :: state);
-    ])
+    ]
+    |> List.filter (fun x -> not (has_visited grid visited_grid x)))
 
 let[@warning "-32"] print_point (x, y) = Printf.printf "(%d, %d)" x y
 
@@ -80,13 +79,10 @@ let part1 (grid, start_pos) =
 
 let part2 (grid, start_pos) =
   let cost = part1 (grid, start_pos) in
-  let visited_grid = Array.make (Aoc.Grid.length grid * 4) max_int in
+  let visited_grid = Array.make (Aoc.Grid.length grid * 4) cost in
   let rec impl acc lst =
     match
-      dijkstra
-        (visit_max grid visited_grid cost)
-        (check_end2 grid visited_grid)
-        lst
+      dijkstra (visit_max grid visited_grid) (check_end2 grid visited_grid) lst
     with
     | None -> acc
     | Some (_, states, remainder) ->