diff --git a/2023/day20.py b/2023/day20.py
new file mode 100644
index 0000000..6cc1eb8
--- /dev/null
+++ b/2023/day20.py
@@ -0,0 +1,108 @@
+import fileinput
+from collections import defaultdict, Counter, deque
+from itertools import count
+
+from utils import mul
+
+
+# Parse problem input.
+broadcaster = []
+flip_flops = defaultdict(list)
+conjunctions = defaultdict(list)
+graph = defaultdict(list)
+
+for line in fileinput.input():
+    line = line.strip()
+    if line.startswith('broadcaster'):
+        outputs = line.split(' -> ')[1]
+        for out in outputs.split(', '):
+            broadcaster.append(out)
+
+    elif line.startswith('%'):
+        mod, outputs = line.split(' -> ')
+        mod = mod[1:]
+        for out in outputs.split(', '):
+            flip_flops[mod].append(out)
+            graph[out].append(mod)
+
+    elif line.startswith('&'):
+        mod, outputs = line.split(' -> ')
+        mod = mod[1:]
+        for out in outputs.split(', '):
+            conjunctions[mod].append(out)
+            graph[out].append(mod)
+
+
+def press_button(state):
+    # Start the cycle with the broadcaster receiving a
+    # low pulse from the button.
+    horizon = deque([('broadcaster', False, 'button')])
+
+    while horizon:
+        dst, pulse, frm = horizon.popleft()
+
+        # Output all pulses to be examined.
+        yield dst, pulse
+
+        if dst == 'broadcaster':
+            for r in broadcaster:
+                horizon.append((r, pulse, dst))
+
+        elif dst in flip_flops:
+            # If a flip-flop receives a high pulse, do nothing.
+            if pulse is True:
+                continue
+
+            # Invert the state of the flip-flop.
+            STATE[dst] = not STATE[dst]
+
+            # Broadcast the new state to all output modules.
+            for r in flip_flops[dst]:
+                horizon.append((r, STATE[dst], dst))
+
+        elif dst in conjunctions:
+            # Set memory of this pulse.
+            STATE[dst][frm] = pulse
+
+            # If memory is all high pulses...
+            for inp, mem in STATE[dst].items():
+                if not mem:
+                    break
+            else:
+                # ...send a low pulse to all output modules.
+                for r in conjunctions[dst]:
+                    horizon.append((r, False, dst))
+
+                continue
+
+            # Otherwise, send a high pulse to all output modules.
+            for r in conjunctions[dst]:
+                horizon.append((r, True, dst))
+
+
+# Solve problem.
+STATE = {k: False for k in flip_flops}
+
+for mod in conjunctions:
+    STATE[mod] = {inp: False for inp in graph[mod]}
+
+# Need to find the aligned cycle of the four modules that
+# feed into conjunction X, where X feeds into `rx`.
+key_regs = graph[graph['rx'][0]]
+cycle_lens = {mod: -1 for mod in key_regs}
+
+pulse_counts = Counter()
+
+for cycle in count(start=1):
+    for module, pulse in press_button(STATE):
+        if pulse is False and cycle_lens.get(module) == -1:
+            cycle_lens[module] = cycle
+
+        if cycle <= 1000:
+            pulse_counts[pulse] += 1
+
+    if all(v != -1 for v in cycle_lens.values()):
+        break
+
+print("Part 1:", mul(pulse_counts.values()))
+print("Part 2:", mul(cycle_lens.values()))