diff --git a/2021/d19.py b/2021/d19.py
new file mode 100644
index 0000000..bc3820b
--- /dev/null
+++ b/2021/d19.py
@@ -0,0 +1,121 @@
+from lib import get_data
+from lib import ints
+from collections import defaultdict
+from itertools import permutations, product
+
+V3 = tuple[int, int, int]
+
+data = get_data(__file__)
+scanners = []
+for block in data.split("\n\n"):
+    scanner = []
+    for line in block.splitlines()[1:]:
+        a, b, c = ints(line)
+        scanner.append((a, b, c))
+    scanners.append(scanner)
+
+
+def rotate(vi: V3) -> list[V3]:
+    r = []
+    for p in permutations(vi):
+        for f in product([1, -1], repeat=3):
+            v = tuple([a * b for a, b in zip(p, f)])
+            r.append(v)
+    return r
+
+
+assert len(rotate((8, 0, 7))) == 48
+
+
+def sub(a: V3, b: V3) -> V3:
+    return a[0] - b[0], a[1] - b[1], a[2] - b[2]
+
+
+def add(a: V3, b: V3) -> V3:
+    return a[0] + b[0], a[1] + b[1], a[2] + b[2]
+
+
+def relative(scanner: list[V3]):
+    d = defaultdict(list)
+    for i in range(len(scanner)):
+        for j in range(i + 1, len(scanner)):
+            for ii, jj in [(i, j), (j, i)]:
+                a, b = scanner[ii], scanner[jj]
+                delta = sub(a, b)
+                d[delta].append((a, b))
+    return d
+
+
+def overlap(scanner_1, scanner_2):
+    expected_overlaps = 15
+    r1 = relative(scanner_1)
+    scanners_2 = []
+    for scanner in list(zip(*list(map(rotate, scanner_2)))):
+        os = set()
+        r2 = relative(scanner)
+        # number of bacon pairs that have the same offset
+        t = sum(1 for k1 in r1.keys() if k1 in r2)
+        if t >= expected_overlaps:
+            for k1, v1 in r1.items():
+                if k1 in r2:
+                    ((abs1, abs2),) = v1
+                    ((rel1, rel2),) = r2[k1]
+                    os.add(sub(abs1, rel1))
+                    os.add(sub(abs2, rel2))
+            if len(os) == 1:
+                # found the right orientation for scanner_2
+                scanners_2.append((os.pop(), scanner))
+            else:
+                r2 = None
+        else:
+            r2 = None
+
+    if len(scanners_2) == 0:
+        return None
+    ((orig_2, scanner_2_rel),) = scanners_2
+    scanner_2_abs = [add(orig_2, b) for b in scanner_2_rel]
+    return orig_2, scanner_2_abs
+
+
+origs = [(0, 0, 0)]
+todo = set(range(len(scanners)))
+done = set([0]) if 0 in todo else set([todo.pop()])
+todo.discard(0)
+while todo:
+    for i in range(len(scanners)):
+        for j in range(len(scanners)):
+            if i == j:
+                continue
+            if i not in done:
+                continue
+            if j in done:
+                continue
+            r = overlap(scanners[i], scanners[j])
+
+            if r is None:
+                continue
+            o, s2 = r
+            origs.append(o)
+            no = len(set(scanners[i]).intersection(s2))
+            if no >= 12:
+                scanners[j] = s2
+                done.add(j)
+                todo.discard(j)
+                # print(f"{i} < {no} > {j} at {o}")
+
+
+all = []
+for s in scanners:
+    all += s
+print(len(set(all)))
+
+
+def mdist(a, b):
+    return sum(abs(aa - bb) for aa, bb in zip(a, b))
+
+
+m = 0
+for i in range(len(origs)):
+    for j in range(i + 1, len(origs)):
+        m = max(m, mdist(origs[i], origs[j]))
+print(m)
diff --git a/README.md b/README.md
index be2270a..95cdd5c 100644
--- a/README.md
+++ b/README.md
@@ -190,7 +190,7 @@ Solutions and utility script for Advent of Code challenges in Python.
 - Day 16:  50:01   (Way too slow. Was non-trivial but fun. Much better was feasible.)
 - Day 17:  21:59   (Not tricky again but struggling for no reason.)
 - Day 18: 162:00   (I couldn't figure out how to solve it as a tree so I did the basic way.)
-- Day 19:
+- Day 19:   days   (Super hard for me but super fun ultimately once I had the right approach.)
 - Day 20: 105:00   (That wasn't easy but was able to solve in one go.)
 - Day 21:  37:45   (Wasn't hard but I was just too slow.)
 - Day 22: 142:00   (Wonderful problem and hard for me but learned something new for sure.)