Update readme and clean up day 20.

README.md

@@ -2,7 +2,8 @@
 
 - Day 1: 40:00 (I don't know what I am doing.)
 - Day 2: 14:15 (Okay, but far way from leaderboard.)
-- Day 3: 1st 20:00, 2nd 70:00... (I had a logic error that took me a while to find.)
+- Day 3: 1st 20:00, 2nd 70:00... (I had a logic error that took me a while to
+  find.)
 - Day 4: 1st 9:06, 2nd 22:31; it wasn't hard but I didn't think quick enough :/
 - Day 5: 1st 25:00, 2nd 1:55:00; Required patience and accuracy
 - Day 6: 13:54; I was slow because I thought it is much harder?
@@ -10,8 +11,10 @@
 - Day 8: 25:00; I was doing pretty decent here.
 - Day 9: 57:00; my input parse function did not consider negative values...
 - Day 10: 180:00; this one was hard for me.
-- Day 11: 68:00; okay but not elegant and way too slow ofc; x-ray solution would have been neat
-- Day 12: 52:00 and 22:00 for leaderboard; had the right idea and I am good at this type of problem
+- Day 11: 68:00; okay but not elegant and way too slow ofc; x-ray solution
+  would have been neat
+- Day 12: 52:00 and 22:00 for leaderboard; had the right idea and I am good at
+  this type of problem
 - Day 13: 90:00; pretty straightforward  but way too slow
 - Day 14: 5:55 for first and then 48:00; straightforward but slow, ofc
 - Day 15: 4:30 and 31:20; more reading comprehension than programming
@@ -22,4 +25,11 @@
   but didn't realize that I have to compute the outer edges for a while and
   after I did, I still got clockwise/counter-clockwise issues. They could have
   made it meaner by using different clock directions for example and input.
-- Day 19: 
+- Day 19: This one was pretty straightforward and required the interval
+  technique we applied earlier.
+- Day 20: Part 2 was tough. I had the right idea of printing out the periods of
+  the input conjunction gate pretty early, but then messed up the
+  implementation and thought it wasn't gonna work. Spent a half day thinking up
+  something else before returning to the idea and it worked flawlessly.
+- Day 21: 
+- Day 22: 

d20.py

@@ -1,5 +1,6 @@
 from lib import *
 from math import lcm
+from collections import deque
 
 EXAMPLE = """
 broadcaster -> a, b, c
@@ -25,10 +26,9 @@ def visualize(modules):
                 f.write(" " + m[1] + ' -> ' + cm + "\n")
         f.write("}")
 
-def solve(i: Input, second=False):
-    res = 0
+def solve(input: Input, second=False):
     modules = {}
-    for line in i.lines():
+    for line in input.lines():
         if not line: continue
         src, dsts = line.split(" -> ")
         dsts = dsts.split(", ")
@@ -48,17 +48,17 @@ def solve(i: Input, second=False):
 
     if second:
         # visualize(modules)
-        periods = {d: [] for d in modules["kh"][2].keys()}
+        (feed,) = [m[1] for m in modules.values() if "rx" in m[3]]
+        periods = {d: [] for d in modules[feed][2].keys()}
         BUTTON_PUSHES = 10000
     else:
         BUTTON_PUSHES = 1000
 
     lo, hi = 0, 0
     for i in range(BUTTON_PUSHES):
-        qs = [("button module", "broadcaster", 0)]
+        qs = deque([("button module", "broadcaster", 0)])
         while qs:
-            src, dst, sig = qs[0]
-            qs = qs[1:]
+            src, dst, sig = qs.popleft()
 
             if sig == 0:
                 lo += 1
@@ -87,7 +87,7 @@ def solve(i: Input, second=False):
 
             if new_pulse is not None:
                 for nxtdst in m[3]:
-                    if second and nxtdst == "kh" and new_pulse == 1:
+                    if second and nxtdst == feed and new_pulse == 1:
                         # print(f"{i:>4}: {dst[:4]:>4} -{new_pulse}> {nxtdst}")
                         periods[dst].append(i)
                     qs.append((dst, nxtdst, new_pulse))