2020/19p1

y2020/p19.py

+import re
+import sys
+
+
+def recurse(rule):
+    return re.sub(r'(\d+)', lambda m: f'({recurse(rules[m.group(1)])})', rule)
+
+
+text = sys.stdin.read()
+rules, stuff = text.split('\n\n')
+rules = dict([ln.split(': ') for ln in rules.splitlines()])
+
+ans = 0
+rex = re.compile(recurse(rules['0']).replace('"', '').replace(' ', '') + '$')
+for line in text.splitlines():
+    ans += bool(rex.match(line))
+print(ans)