change structure of folders

AoC2020/code/AoC19.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+
+import sys
+import re
+
+def parse_rules(lines):
+    rules =  {}
+    for line in lines:
+        rule, pattern = line.split(':')
+        alternatives = pattern.split('|')
+        rules[int(rule)] = [a.strip(' ').split(' ') for a in alternatives]
+    return rules
+
+def memo(f):
+   mem = {}
+   def helper(x):
+      if x not in mem: mem[x] = f(x)
+      return mem[x]
+   return helper
+
+@memo
+def expr(rule):
+    if rule == 8:
+        return expr(42) + '+'
+    if rule == 11:
+        return '(?:' + expr(42) + '(?=a*(\1?+b)b*(\2?+c)))+\1' + expr(31) + ')'
+    global rules
+    if type(rule) is str: 
+        try: rule = int(rule)
+        except ValueError: return rule[1]
+    pattern = rules[rule]
+    res = ["".join(expr(dep) for dep in alt) for alt in pattern]
+    if len(res) == 1: return res[0]
+    return "(" + "|".join(res) + ")"
+
+if __name__ == '__main__':
+    rules, messages = open(sys.argv[1]).read().split('\n\n')
+    rules = parse_rules(rules.split('\n'))
+    count = 0
+    messages = messages.split("\n")
+    for m in messages: 
+        if bool(re.match('^' + expr(0) + '$', m)):
+            count += 1
+    print(count)