Solve day 20 and day 21 part 1.

d21.py

@@ -0,0 +1,55 @@
+from lib import *
+
+EXAMPLE = """
+...........
+.....###.#.
+.###.##..#.
+..#.#...#..
+....#.#....
+.##..S####.
+.##..#...#.
+.......##..
+.##.#.####.
+.##..##.##.
+...........
+"""
+
+def solve(i: Input, second=False):
+    res = 0
+    g = i.grid2()
+    s = g.find('S')[0]
+    g[s] = 'O'
+    # steps = 64
+    steps = 26501365
+    seen = set()
+    for i in range(steps):
+        os = tuple(g.find('O'))
+        if os in seen:
+            seen.add(os)
+            print(f"SEEN {i}")
+            break
+
+        for o in os:
+            g[o] = '.'
+
+        for o in os:
+            for nb in g.neighbors_ort(o):
+                if not g[nb] == "#":
+                    g[nb] = 'O'
+    return len(g.find('O'))
+
+def main():
+    DAY_INPUT = "i21.txt"
+
+    print("Example  1:", solve(Input(EXAMPLE)))
+    print("Solution 1:", solve(Input(DAY_INPUT)))
+    return
+
+    print("Example  2:", solve(Input(EXAMPLE), True))
+    return
+
+    print("Solution 2:", solve(Input(DAY_INPUT), True))
+    return
+
+if __name__ == "__main__":
+    main()