Do day 14.

d14.py

@@ -0,0 +1,88 @@
+from lib import *
+
+EXAMPLE = """
+O....#....
+O.OO#....#
+.....##...
+OO.#O....O
+.O.....O#.
+O.#..O.#.#
+..O..#O..O
+.......O..
+#....###..
+#OO..#....
+"""
+
+def get_nth_elem(xs, n):
+    """ Find the nth element of a repeating sequence. """
+    found = set()
+    x = None
+    for (i, x) in enumerate(xs):
+        if x in found:
+            break
+        found.add(x)
+    if i is None:
+        raise Exception("No repeating sequence.")
+    first_repeat = i
+    initial_sequence_length = xs.index(x)
+    repeating_sequence_length = first_repeat - xs.index(x)
+
+    adjusted_n = n - initial_sequence_length
+    position_in_repeating_sequence = adjusted_n % repeating_sequence_length
+    element = xs[initial_sequence_length + position_in_repeating_sequence]
+    return element
+
+def solve(i: Input, second=False):
+    res = 0
+    g = i.grid2()
+    if second:
+        dirs = [Grid2D.N, Grid2D.W, Grid2D.S, Grid2D.E]
+        cycles = 1000000000
+    else:
+        dirs = [Grid2D.N]
+        cycles = 1
+
+    fs = {}
+    v = []
+    for i in range(cycles):
+        h = hash(tuple(g.find('O')))
+        fs[h] = tuple(g.find('O'))
+        v.append(h)
+        if v.count(h) > 1:
+            break
+        for d in dirs:
+            moved = True
+            while moved:
+                moved = False
+                for r in g.find('O'):
+                    rn = add2(r, d)
+                    if rn in g and g[rn] == '.':
+                        g[r] = '.'
+                        g[rn] = 'O'
+                        moved = True
+
+    if second:
+        h = get_nth_elem(v, 1000000000)
+        os = fs[h]
+        for r, c in os:
+            s = g.n_rows - r
+            res += s
+    else:
+        for r, c in g.find('O'):
+            s = g.n_rows - r
+            res += s
+    return res
+
+def main():
+    DAY_INPUT = "i14.txt"
+
+    print("Example  1:", solve(Input(EXAMPLE)))
+    print("Solution 1:", solve(Input(DAY_INPUT)))
+    # 5:55
+
+    print("Example  2:", solve(Input(EXAMPLE), True))
+    print("Solution 2:", solve(Input(DAY_INPUT), True))
+    # 48:00
+
+if __name__ == "__main__":
+    main()