2020/19

y2020/p19.py

 
 
 def recurse(rule):
-    return re.sub(r'(\d+)', lambda m: f'({recurse(rules[m.group(1)])})', rule)
+    def replacer(m):
+        return f'({recurse(rules[m.group(1)])})'
+    return re.sub(r'(\d+)', replacer, rule).replace('"', '').replace(' ', '')
 
 
 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)
+rule0 = re.compile(recurse(rules['0'])).fullmatch
+print(sum(bool(rule0(line)) for line in stuff.splitlines()))
+
+
+def rule8(line):
+    # 8 = 42 | 42 8
+    for i in range(1, len(line) + 1):
+        a, b = line[:i], line[i:]
+        if rule42(a):
+            if not b or rule8(b):
+                return True
+
+
+def rule11(line):
+    # 11 = 42 31 | 42 11 31
+    for i in range(1, len(line) + 1):
+        for j in range(i, len(line)):
+            a, b, c = line[:i], line[i:j], line[j:]
+            if rule42(a) and rule31(c):
+                if not b or rule11(b):
+                    return True
+
+
+rule42 = re.compile(recurse(rules['42'])).fullmatch
+rule31 = re.compile(recurse(rules['31'])).fullmatch
+# 0 = 8 11
+ans2 = 0
+for ln in stuff.splitlines():
+    valid = any(rule8(ln[:i]) and rule11(ln[i:]) for i in range(1, len(ln)))
+    ans2 += bool(valid)
+print(ans2)