Solve 2016:18 p1-2 "Like a Rogue"

Figured out that the center position did not matter,
as long as left hand side tile and right hand side
tile on previous row are not equal.

Also tried to find a recurring pattern to speed
p2 up a bit, but it seems it does not have a
recurring pattern in the 400 000s first rows.

2016-python2/output/day_18.py

@@ -0,0 +1,32 @@
+def solve(data):
+    cols = len(data)
+    prevrow = [t == "." for t in data]
+    p1 = sum(prevrow) + sum(
+        sum(prevrow := [issafe(prevrow, i) for i in range(cols)]) for _ in range(39)
+    )
+    p2 = p1 + sum(
+        sum(prevrow := [issafe(prevrow, i) for i in range(cols)])
+        for _ in range(400_000 - 40)
+    )
+    return p1, p2
+
+
+def issafe(row, i):
+    match i:
+        case 0:
+            return row[1]
+        case n if n == len(row) - 1:
+            return row[-2]
+        case _:
+            lt, rt = row[i - 1], row[i + 1]
+            return not lt != rt
+
+
+if __name__ == "__main__":
+    with open("./input/18.txt", "r") as f:
+        inp = f.read().strip()
+
+    p1, p2 = solve(inp)
+
+    print(p1)
+    print(p2)