Add day 20 part 2

day20/part2.txt

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+Part 2 wasn't really code-based. I made a graphviz visualization of my input (script to do so is in this repo)
+and then I stared at it with intent, until I realized there were four "sections" that needed to line up at the
+same time. I realized this seemed like an LCM problem, so I found all the times that the "sections" emitted
+to the central conjunctions, and took the LCM of that, since this is cyclical.
+
+I left my print statements in the solution so you can try it :)

day20/todot.py

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+import sys
+import typing
+import string
+
+def parseModules(f: typing.TextIO) -> dict[str, list[str]]:
+    modules = {}
+    for line in f:
+        (key, lineModules) = line.strip().split(' -> ')
+        modules[key] = lineModules.split(', ')
+
+    for fullName in modules:
+        for children in modules.values():
+            for (i, module) in enumerate(children):
+                if fullName == f"&{module}" or fullName == f"%{module}":
+                    children[i] = fullName
+
+    return modules
+
+def alpha_only(s: str) -> str:
+    return ''.join(char for char in s if char in string.ascii_letters)
+
+
+def main():
+    if len(sys.argv) != 2:
+        print(f"Usage: {sys.argv[0]} input.txt")
+
+    with open(sys.argv[1]) as f:
+        modules = parseModules(f)
+
+    import pprint
+    print("graph {")
+    for node in modules.keys():
+        print(f'  {alpha_only(node)}[label="{node}"]')
+
+    for parent, children in modules.items():
+        print(f"  {alpha_only(parent)} -> {{{' '.join(alpha_only(child) for child in children)}}}")
+
+    print("}")
+
+
+
+
+
+if __name__ == "__main__":
+    main()