Solve day 20 and day 21 part 1.

d20.py

@@ -0,0 +1,108 @@
+from lib import *
+from math import lcm
+
+EXAMPLE = """
+broadcaster -> a, b, c
+%a -> b
+%b -> c
+%c -> inv
+&inv -> a
+"""
+
+EXAMPLE2 = """
+broadcaster -> a
+%a -> inv, con
+&inv -> b
+%b -> con
+&con -> output
+"""
+
+def visualize(modules):
+    with open("g20.dot", 'w') as f:
+        f.write("digraph G {\n")
+        for m in modules.values():
+            for cm in m[3]:
+                f.write(" " + m[1] + ' -> ' + cm + "\n")
+        f.write("}")
+
+def solve(i: Input, second=False):
+    res = 0
+    modules = {}
+    for line in i.lines():
+        if not line: continue
+        src, dsts = line.split(" -> ")
+        dsts = dsts.split(", ")
+        if src.startswith("%"):  # flip-flop
+            modules[src[1:]] = [src[0], src[1:], 0, dsts]
+        elif src.startswith("&"):  # conjunction
+            modules[src[1:]] = [src[0], src[1:], {}, dsts]
+        elif src.startswith("broadcaster"):
+            modules[src] = ["b", src, 0, dsts]
+        else:
+            raise Exception()
+
+    for m in modules.values():
+        for d in m[3]:
+            if d in modules and modules[d][0] == "&":
+                modules[d][2][m[1]] = 0
+
+    if second:
+        # visualize(modules)
+        periods = {d: [] for d in modules["kh"][2].keys()}
+        BUTTON_PUSHES = 10000
+    else:
+        BUTTON_PUSHES = 1000
+
+    lo, hi = 0, 0
+    for i in range(BUTTON_PUSHES):
+        qs = [("button module", "broadcaster", 0)]
+        while qs:
+            src, dst, sig = qs[0]
+            qs = qs[1:]
+
+            if sig == 0:
+                lo += 1
+            else:
+                hi += 1
+
+            if not dst in modules:
+                continue
+
+            m = modules[dst]
+            new_pulse = None
+            if m[0] == "b":
+                new_pulse = 0
+            elif m[0] == "%":
+                if sig == 0:
+                    m[2] = (m[2] + 1) % 2
+                    new_pulse = m[2]
+            elif m[0] == "&":
+                m[2][src] = sig
+                if all(s == 1 for s in m[2].values()):
+                    new_pulse = 0
+                else:
+                    new_pulse = 1
+            else:
+                raise Exception()
+
+            if new_pulse is not None:
+                for nxtdst in m[3]:
+                    if second and nxtdst == "kh" and new_pulse == 1:
+                        # print(f"{i:>4}: {dst[:4]:>4} -{new_pulse}> {nxtdst}")
+                        periods[dst].append(i)
+                    qs.append((dst, nxtdst, new_pulse))
+    if second:
+        # print(periods)
+        # Yeah, we got a bit lucky that this works, I guess, but it does.
+        return lcm(*[v[1] - v[0] for v in periods.values()])
+    return lo * hi
+
+def main():
+    DAY_INPUT = "i20.txt"
+    print("Example  1:", solve(Input(EXAMPLE)))
+    print("Example  2:", solve(Input(EXAMPLE2)))
+    print("Solution 1:", solve(Input(DAY_INPUT)))
+    print("Solution 2:", solve(Input(DAY_INPUT), True))
+
+if __name__ == "__main__":
+    main()

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()