diff --git a/.aoc_tiles/tiles/2024/20.png b/.aoc_tiles/tiles/2024/20.png
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index 0000000..cd5c182
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diff --git a/2024/20/example b/2024/20/example
new file mode 100644
index 0000000..c097dae
--- /dev/null
+++ b/2024/20/example
@@ -0,0 +1,15 @@
+###############
+#...#...#.....#
+#.#.#.#.#.###.#
+#S#...#.#.#...#
+#######.#.#.###
+#######.#.#...#
+#######.#.###.#
+###..E#...#...#
+###.#######.###
+#...###...#...#
+#.#####.#.###.#
+#.#...#.#.#...#
+#.#.#.#.#.#.###
+#...#...#...###
+###############
diff --git a/2024/20/script.py b/2024/20/script.py
new file mode 100644
index 0000000..39e94fe
--- /dev/null
+++ b/2024/20/script.py
@@ -0,0 +1,98 @@
+from GhostyUtils import aoc
+from GhostyUtils.grid import Grid
+from GhostyUtils.vec2 import Vec2, manhattan_distance as mh_dist
+from GhostyUtils.pathfinding import bfs
+from collections import defaultdict
+from functools import partial
+
+
+aoc.argparser.add_argument("-s", "--save", type=int, default=100, help="picoseconds to save")
+
+
+# non-walls 1 space UDLR from pos
+def neighbours(pos: tuple, grid: Grid) -> list[tuple]:
+ return [n for n in grid.neighbours(pos, diagonal=False) if grid[n] != '#']
+
+
+# non-walls behind walls, 2 spaces UDLR from pos
+def cheat(pos: tuple, grid: Grid) -> list[Vec2]:
+ pos = Vec2(pos)
+
+ def end_pos(pos, n):
+ return pos+(n-pos)*2
+
+ return [end_pos(pos, n) for n in grid.neighbours(pos, diagonal=False)
+ if grid[n] == '#' and grid.in_bounds(end_pos(pos, n)) and grid[end_pos(pos, n)] != '#']
+
+
+def cheat_savings(saves: dict[int], minimum: int):
+ for saving, cheats in sorted(list(saves.items())):
+ if saving < minimum:
+ continue
+ print(f"There are {cheats} cheats that save {saving} picoseconds.")
+
+
+def main():
+ racetrack = Grid(aoc.read_lines())
+ start = racetrack.find('S')
+ end = racetrack.find('E')
+ target = aoc.args.save
+
+ neighbours_func = partial(neighbours, grid=racetrack)
+ clean_path = next(bfs(start, end, neighbours=neighbours_func))
+ clean_time = len(clean_path)
+ # map clean path positions to their index in the list, for faster lookup
+ clean_path_index = {pos: i for i, pos in enumerate(clean_path)}
+
+ # print the clean path
+ if aoc.args.progress or aoc.args.verbose:
+ overlays = [
+ {path: '.' for path in clean_path},
+ {start: 'S', end: 'E'},
+ ]
+ print(racetrack.render_with_overlays(overlays))
+ print(f"clean time: {clean_time} picoseconds")
+
+ saves = defaultdict(int)
+ cheats = {}
+ for i, pos in enumerate(clean_path[:-1]):
+ for c in cheat(pos, racetrack):
+ # skip cheats that take us backwards
+ if clean_path_index[c.as_tuple()] < i:
+ continue
+
+ # calculate the time saved
+ saved = -(i - clean_path_index[c.as_tuple()] + 2)
+ saves[saved] += 1
+ cheats[(pos, c.as_tuple())] = saved
+
+ # draw the cheats on the map
+ if aoc.args.verbose:
+ overlays.append({(pos+(c-pos)/2).as_tuple(): '1',
+ c.as_tuple(): '2'})
+ print(racetrack.render_with_overlays(overlays))
+ print(f"^ saves {saved} picoseconds")
+ overlays.pop()
+
+ if aoc.args.progress or aoc.args.verbose:
+ cheat_savings(saves, target)
+ print(f"p1: {sum(times for saved, times in saves.items() if saved >= 100)}")
+
+ saves = defaultdict(int)
+ for i, pos in enumerate(clean_path[:-target]):
+ # loop over path positions that are over 100 positions forward along the path and under
+ # 20 manhattan distance away from the current position
+ for candidate, md in filter(lambda md: md[1] <= 20,
+ ((other, mh_dist(pos, other))
+ for other in clean_path[i+target:])):
+ # calculate the time saved
+ saved = -(i - clean_path_index[candidate] + md)
+ saves[saved] += 1
+
+ if aoc.args.progress or aoc.args.verbose:
+ cheat_savings(saves, target)
+ print(f"p2: {sum(times for saved, times in saves.items() if saved >= target)}")
+
+
+if __name__ == "__main__":
+ main()
diff --git a/README.md b/README.md
index 0706a66..d71534b 100644
--- a/README.md
+++ b/README.md
@@ -3,10 +3,10 @@ My solutions to the yearly Advents of Code
- Advent of Code - 197/488 ⭐
+ Advent of Code - 199/490 ⭐
- 2024 - 36 ⭐ - Python
+ 2024 - 38 ⭐ - Python
@@ -65,6 +65,9 @@ My solutions to the yearly Advents of Code
+
+ 
+
2023 - 47 ⭐ - Python