Solve 2020 day 24 and 25 and 2018 day 23 part 2

2020/d24.py

@@ -0,0 +1,59 @@
+from lib import get_data, add2
+from collections import defaultdict
+
+DIRS = {
+    "e": (0, 2),
+    "w": (0, -2),
+    "se": (1, 1),
+    "sw": (1, -1),
+    "nw": (-1, -1),
+    "ne": (-1, 1),
+}
+
+data = get_data(__file__)
+
+tiles_black = set()
+
+for row in data.splitlines():
+    row = row.strip()
+    i = 0
+    pos = (0, 0)
+    while i < len(row):
+        d = None
+        if row[i] in DIRS:
+            d = DIRS[row[i]]
+            i += 1
+        elif "".join(row[i : i + 2]) in DIRS:
+            d = DIRS["".join(row[i : i + 2])]
+            i += 2
+        else:
+            assert False
+        assert d is not None
+        pos = add2(pos, d)
+    if pos in tiles_black:
+        tiles_black.remove(pos)
+    else:
+        tiles_black.add(pos)
+
+print(len(tiles_black))
+
+for _ in range(100):
+    nbs = defaultdict(int)
+    for bt in tiles_black:
+        for d in DIRS.values():
+            nb = add2(bt, d)
+            nbs[nb] += 1
+    new_tiles_black = set()
+    for pos, count in nbs.items():
+        if pos in tiles_black:
+            if count == 0 or count > 2:
+                pass
+            else:
+                new_tiles_black.add(pos)
+        else:
+            if count == 2:
+                new_tiles_black.add(pos)
+
+    tiles_black = new_tiles_black
+
+print(len(tiles_black))

2020/d25.py

@@ -0,0 +1,32 @@
+from lib import get_data, ints
+
+data = get_data(__file__)
+a, b = ints(data)
+
+v = 1
+subject_number = 7
+al, bl = None, None
+
+for loop in range(100_000_000):
+    v *= subject_number
+    v %= 20201227
+    if al is None and v == a:
+        al = loop + 1
+    if bl is None and v == b:
+        bl = loop + 1
+
+    if al and bl:
+        break
+
+assert al is not None
+assert bl is not None
+# print(al, bl)
+
+v = 1
+subject_number = b
+for _ in range(al):
+    v *= subject_number
+    v %= 20201227
+
+print(v)
+