2020: d19: ex2: add solution

2020/d19/ex2/ex2.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python
+
+import itertools
+import re
+import sys
+from typing import Dict, List
+
+
+def parse_rule(raw_rules: List[str]) -> str:
+    parsed: Dict[int, str] = {}
+    rules = {int(num): rule.strip() for num, rule in (i.split(":") for i in raw_rules)}
+
+    for n, r in rules.items():
+        if '"' not in r:
+            continue
+        parsed[n] = r.replace('"', "")
+
+    while 0 not in parsed:
+        for num in parsed:
+            if num not in rules:
+                continue
+            rules.pop(num)
+
+        for num, r in rules.items():
+            nums = list(reversed(sorted(map(int, re.findall("(\\d+)", r)))))
+            if all(n in parsed for n in nums):
+                for n in nums:
+                    r = re.sub(str(n), parsed[n], r)  # Bigger numbers replaced first
+                r = r.replace(" ", "{x}" if num == 11 else "")
+                if num == 11:
+                    r = "(" + r + "{x})"
+                r = "(" + r + ")"
+                if num == 8:
+                    r = "(" + r + "+)"
+                parsed[num] = r
+    return parsed[0]
+
+
+def solve(raw: List[str]) -> int:
+    pattern = parse_rule(list(itertools.takewhile(len, raw)))
+
+    def matches(repeats: int) -> int:
+        pat = re.compile(pattern.replace("x", str(repeats)))
+        return sum(
+            pat.fullmatch(line) is not None for line in itertools.dropwhile(len, raw)
+        )
+
+    return sum(itertools.takewhile(bool, map(matches, itertools.count(1))))
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()