1 files changed, 47 insertions, 0 deletions
diff --git a/2024/18/python.py b/2024/18/python.py
new file mode 100755
index 0000000..1f987c6
--- /dev/null
+++ b/2024/18/python.py
@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+
+from bisect import bisect_left
+from collections import deque
+from fileinput import input
+
+coords = [line.strip().split(",") for line in input()]
+grid = {complex(int(x), int(y)): t for t, [x, y] in enumerate(coords)}
+
+
+def solve(size, delay):
+    q = deque([(0, 0)])
+    seen = set()
+    while q:
+        curr, t = q.popleft()
+        if curr in seen:
+            continue
+        if curr == complex(size, size):
+            return t
+        seen.add(curr)
+
+        for d in [1, -1, 1j, -1j]:
+            x = curr + d
+            if not (0 <= x.real <= size and 0 <= x.imag <= size):
+                continue
+            if x in grid and grid[x] < delay:
+                continue
+            q.append((x, t + 1))
+    return None
+
+
+silver = solve(70, 1024)
+# silver = solve(6, 12)  # test.txt
+
+gold = ",".join(
+    coords[
+        bisect_left(
+            list(range(len(grid))),
+            True,
+            key=lambda x: solve(70, x) is None,
+        )
+        - 1
+    ]
+)
+
+print("silver:", silver)
+print("gold:", gold)