Add solution to 2024-12-06

Author: fuglede

2024/day06/solutions.py

@@ -0,0 +1,39 @@
+with open("input") as f:
+    ls = f.read().strip().split("\n")
+
+board = {i + 1j * j: x for i, l in enumerate(ls) for j, x in enumerate(l)}
+
+# Part 1
+start = next(w for w, x in board.items() if x == "^")
+walls = {w for w, x in board.items() if x == "#"}
+seen = set()
+z = start
+dz = -1
+while z in board:
+    seen.add(z)
+    if z + dz in walls:
+        dz *= -1j
+        continue
+    z += dz
+
+print(len(seen))
+
+
+# Part 2
+def loops(x):
+    new_walls = walls | {x}
+    z = start
+    dz = -1
+    seen = set()
+    while z in board:
+        if (z, dz) in seen:
+            return True
+        seen.add((z, dz))
+        if z + dz in new_walls:
+            dz *= -1j
+            continue
+        z += dz
+    return False
+
+
+print(sum(map(loops, seen)))