Day 19, sloooow

2021/day19.py

@@ -0,0 +1,97 @@
+from collections import defaultdict
+from itertools import combinations, permutations
+
+with open("input19.txt") as f:
+    lines = [line.rstrip() for line in f]
+scanners = []
+for line in lines:
+    if line.startswith("--"):
+        scanner_id = int(line.split()[2])
+        positions = []
+    elif line:
+        positions.append(tuple(map(int, line.split(","))))
+    else:
+        scanners.append((scanner_id, positions))
+scanners.append((scanner_id, positions))
+
+
+def N(x, y, z): return x, y, z
+def X(x, y, z): return x, -z, y
+def Y(x, y, z): return -z, y, x
+def add(v1, v2): return v1[0] + v2[0], v1[1] + v2[1], v1[2] + v2[2]
+def sub(v1, v2): return v1[0] - v2[0], v1[1] - v2[1], v1[2] - v2[2]
+
+
+orientations = [
+    "N", "X", "Y", "XX", "XY", "YX", "YY", "XXX", "XXY", "XYX", "XYY", "YXX",
+    "YYX", "YYY", "XXXY", "XXYX", "XXYY", "XYXX", "XYYY", "YXXX", "YYYX",
+    "XXXYX", "XYXXX", "XYYYX"
+]
+rotations = {k: globals()[k] for k in "NXY"}
+
+
+def orient(x, y, z, orientation):
+    for axis in orientation:
+        x, y, z = rotations[axis[::-1]](x, y, z)
+    return x, y, z
+
+
+overlaps = {}
+oriented = {
+    sb_id: [(o, [orient(*pos, o) for pos in sb]) for o in orientations]
+    for sb_id, sb in scanners
+}
+# Using permutations is slower than combinations but it's simpler to find the
+# transform path after.
+for (sa_id, sa), (sb_id, _) in permutations(scanners, 2):
+    for orientation, osb in oriented[sb_id]:
+        diffs = defaultdict(int)
+        for ax, ay, az in sa:
+            for bx, by, bz in osb:
+                diff = (ax - bx, ay - by, az - bz)
+                diffs[diff] += 1
+                if diffs[diff] >= 12:
+                    overlaps[(sa_id, sb_id)] = (orientation, diff)
+                    break
+            else:
+                continue
+            break
+        else:
+            continue
+        break
+
+
+def find_transform_to_0(from_s):
+    chains = [[p] for p in overlaps if p[0] == from_s]
+    seen = set()
+    while chains:
+        chain = chains.pop(0)
+        if chain[-1][1] == 0:
+            return chain
+        for p in overlaps:
+            if p[0] == chain[-1][1] and p not in seen:
+                seen.add(p)
+                chains.append(chain + [p])
+
+
+def see_as_0(x, y, z, sid):
+    for t in find_transform_to_0(sid):
+        ori, move = overlaps[t[::-1]]
+        x, y, z = add(orient(x, y, z, ori), move)
+    return x, y, z
+
+
+def see_scanner_as_0(sid, sdata):
+    for x, y, z in sdata:
+        yield see_as_0(x, y, z, sid)
+
+
+beacons = set()
+for scanner_id in range(len(scanners)):
+    beacons |= set(list(see_scanner_as_0(*scanners[scanner_id])))
+print(len(beacons))
+scanner_positions = [see_as_0(0, 0, 0, sid) for sid in range(len(scanners))]
+print(max(
+    sum(map(abs, sub(spb, spa)))
+    for spa, spb in combinations(scanner_positions, 2)
+))