Add day10

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

day10/day10.py

@@ -0,0 +1,147 @@
+#!/usr/bin/env python3
+import sys
+from typing import Sequence
+
+
+class ParseError(Exception):
+    def __init__(self, got: str, expected: str):
+        self.got = got
+        self.expected = expected
+        super().__init__(f"expected {repr(expected)} but got {repr(got)} instead")
+
+
+CLOSING = ")]}>"
+
+
+class Parser:
+    def __init__(self, text: str):
+        self.text = text
+        self.ptr = 0
+
+    def reset(self):
+        self.ptr = 0
+
+    @property
+    def is_eof(self) -> bool:
+        return self.ptr >= len(self.text)
+
+    @property
+    def c(self) -> str:
+        if self.is_eof:
+            return ""
+        else:
+            return self.text[self.ptr]
+
+    def adv(self):
+        if self.ptr >= len(self.text):
+            self.ptr = len(self.text)
+        else:
+            self.ptr += 1
+
+    def expect(self, c: str):
+        if c == self.c:
+            self.adv()
+        else:
+            raise ParseError(self.c, c)
+
+    def parse(self):
+        if self.c == "(":
+            self.parse_paren()
+        elif self.c == "[":
+            self.parse_bracket()
+        elif self.c == "{":
+            self.parse_brace()
+        elif self.c == "<":
+            self.parse_angle()
+
+    def parse_paren(self):
+        self.expect("(")
+        while self.c not in CLOSING:
+            self.parse()
+        self.expect(")")
+
+    def parse_bracket(self):
+        self.expect("[")
+        while self.c not in CLOSING:
+            self.parse()
+        self.expect("]")
+
+    def parse_brace(self):
+        self.expect("{")
+        while self.c not in CLOSING:
+            self.parse()
+        self.expect("}")
+
+    def parse_angle(self):
+        self.expect("<")
+        while self.c not in CLOSING:
+            self.parse()
+        self.expect(">")
+
+
+def part1(lines: Sequence[str]):
+    scores = {
+        ")": 3,
+        "]": 57,
+        "}": 1197,
+        ">": 25137,
+        "": 0,
+    }
+    points = 0
+    for line in lines:
+        try:
+            parser = Parser(line)
+            while not parser.is_eof:
+                parser.parse()
+        except ParseError as e:
+            points += scores[e.got]
+    print(points)
+
+
+def part2(lines: Sequence[str]):
+    scores = {
+        ")": 1,
+        "]": 2,
+        "}": 3,
+        ">": 4,
+    }
+    all_points = []
+    for line in lines:
+        completion = ""
+        try:
+            parser = Parser(line)
+            while not parser.is_eof:
+                parser.parse()
+        except ParseError as e:
+            if e.got != "":
+                continue
+            # Try to complete the parse using exceptions :^)
+            parser.text += e.expected
+            completion += e.expected
+            while True:
+                parser.reset()
+                try:
+                    while not parser.is_eof:
+                        parser.parse()
+                    break
+                except ParseError as e:
+                    assert e.expected != ""
+                    parser.text += e.expected
+                    completion += e.expected
+        # Calculate points using the completion
+        points = 0
+        for c in completion:
+            points *= 5
+            points += scores[c]
+
+        all_points += [points]
+    all_points = sorted(all_points)
+    print(all_points[len(all_points) // 2])
+
+
+lines = list(map(str.strip, sys.stdin))
+
+print("Part 1")
+part1(lines)
+print("Part 2")
+part2(lines)