From aeda596ba76e127c9cb2d48d2adc03e62466f302 Mon Sep 17 00:00:00 2001
From: Stefan Nygaard Hansen <stefannygaardhansen@gmail.com>
Date: Wed, 20 Dec 2023 11:23:54 +0100
Subject: [PATCH] Add day20, 2023

---
 2023/day20/input       | 58 +++++++++++++++++++++++++++++++++
 2023/day20/solution.py | 74 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 132 insertions(+)
 create mode 100644 2023/day20/input
 create mode 100644 2023/day20/solution.py

diff --git a/2023/day20/input b/2023/day20/input
new file mode 100644
index 0000000..ff3f47e
--- /dev/null
+++ b/2023/day20/input
@@ -0,0 +1,58 @@
+%sf -> pz, gj
+%zh -> bc, st
+%hk -> bc
+&bc -> mn, zl, xb, mm, dh, hv, gz
+%st -> bc, mm
+%gv -> xf, qq
+%hv -> xb
+%nd -> gj, tr
+%zx -> bx, ms
+%sc -> ks, gj
+%gr -> hn
+%pl -> qq, rh
+%qc -> sf, gj
+%xr -> sc, gj
+%zl -> zh
+&gj -> ks, ld, sg, xr
+%dg -> ll, bx
+%nf -> bc, tg
+%lz -> cv, qq
+%nq -> dg, bx
+%rh -> qq, lp
+%xf -> qq, qj
+%ms -> bx, xh
+%mn -> bc, hv
+&jm -> rx
+%xh -> vt, bx
+%pz -> gj
+%vq -> bt
+%gz -> nf
+%bt -> gr
+&sg -> jm
+%fr -> bx, tb
+&lm -> jm
+%ld -> cl
+%cv -> vq
+%cl -> gj, jf
+%tr -> gj, sz
+%sz -> gj, ld
+%dx -> hk, bc
+%lr -> bx, fr
+%vt -> lr, bx
+%ll -> zx
+broadcaster -> pl, xr, mn, xc
+%lp -> lz
+%mm -> gz
+&qq -> lm, gr, cv, vq, lp, pl, bt
+%xb -> zl
+&bx -> ll, xc, db
+%tb -> bx
+%hn -> gv, qq
+%jf -> qc, gj
+%qj -> qq
+%xc -> bx, pm
+%tg -> bc, dx
+&dh -> jm
+%ks -> nd
+&db -> jm
+%pm -> bx, nq
diff --git a/2023/day20/solution.py b/2023/day20/solution.py
new file mode 100644
index 0000000..651878f
--- /dev/null
+++ b/2023/day20/solution.py
@@ -0,0 +1,74 @@
+from math import lcm
+from functools import reduce
+
+with open("input") as f:
+    inp = f.read().strip().split("\n")
+
+
+type_ = {}
+dests = {} 
+memory = {}
+for line in inp:
+    from_, dest = line.split(" -> ")
+    typ = from_[0]
+    name = from_[1:]
+    if typ == "b":
+        name = from_
+        typ = ""
+    type_[name] = typ
+    dests[name] = dest.split(", ")
+    if typ == "&":
+        memory[name] = {}
+    elif typ == "%":
+        memory[name] = 0
+
+for from_, dests_ in dests.items():
+    for dest in dests_:
+        if dest in type_ and type_[dest] == "&":
+            memory[dest][from_] = 0
+
+
+cycle, n_low, n_high = 0, 0, 0
+def press_button():
+    global cycle
+    global n_low
+    global n_high
+    q = [("button", "broadcaster", 0)]
+    while q:
+        from_, to, pulse = q.pop(0)
+        n_low += 1-pulse
+        n_high += pulse
+        if to not in dests:
+            continue
+        type_to = type_[to]
+        dests_to = dests[to]
+        if type_to == "":
+            for dest in dests_to:
+                q.append((to, dest, 0))
+        elif type_to == "%":
+            if pulse == 0:
+                memory[to] = (memory[to]+1)%2
+                for dest in dests_to:
+                    q.append((to, dest, memory[to]))
+        elif type_to == "&":
+            memory[to][from_] = pulse
+            if to == "jm" and pulse == 1:
+                cycles.append(cycle+1)
+            if all(x == 1 for x in memory[to].values()):
+                for dest in dests_to:
+                    q.append((to, dest, 0))
+            else:
+                for dest in dests_to:
+                    q.append((to, dest, 1))
+    cycle += 1
+
+
+# The module "rx" gets a low pulse if and only module "jm" has last been sent high pulses from modules "dh", "lm", "dg" and "db".
+# We figure out when each of these send high pulses to "jm" and anticipate a cyclic nature.
+cycles = []
+while (len(cycles) < 4):
+    if cycle == 1000:
+        print(n_low*n_high)
+    press_button()
+
+print(reduce(lcm, cycles))
\ No newline at end of file