commit 6d614d6d159f60c4698556c9f413e417973c07a1
parent 605b631b1e31767e3772224d11f14bb18c91aedd
Author: Eamon Caddigan <eamon.caddigan@gmail.com>
Date: Fri, 10 Dec 2021 11:00:44 -0500
Soution to day 10, part 2
Diffstat:
| A | day10_part2.py | | | 69 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
1 file changed, 69 insertions(+), 0 deletions(-)
diff --git a/day10_part2.py b/day10_part2.py
@@ -0,0 +1,69 @@
+#!/usr/bin/env python
+"""Advent of Code 2021, day 10 (part 2): Syntax Scoring
+For part 2, we are completing the 'incomplete' lines and finding the score
+associated with their completion."""
+
+from day10_part1 import (EXAMPLE_INPUT,
+ convert_input_to_list,
+ is_open_bracket,
+ match_bracket)
+from utils import get_puzzle_input
+
+def score_bracket(bracket):
+ """Given a close bracket, return its associated score"""
+ return {')': 1, ']': 2, '}': 3, '>': 4}[bracket]
+
+def score_line(line):
+ """Return the 'score' of an incomplete line, or 0 for lines that are not
+ incomplete or are corrupt"""
+ # The problem description text implies that a line must be incomplete or
+ # corrupt, but I don't trust that's true (it's not explicit enough for me);
+ # I'm going to return a score of 0 for any line that is neither incomplete
+ # nor corrupt (even though there are none in the example input and probably
+ # none in my puzzle input). Just using a loop and stack again.
+ bracket_stack = []
+ line_score = 0
+ # line_score = line_score * 5 + score_bracket(bracket)
+ for bracket in line:
+ if is_open_bracket(bracket):
+ bracket_stack.append(bracket)
+ else:
+ if match_bracket(bracket_stack.pop()) != bracket:
+ # This is a corrupt line, return 0
+ return 0
+
+ # Figure out which brackets are necessary to clear the stack and score the
+ # line. This could be implemented with a list comprehension to run more
+ # quickly, but I find this conceptually simpler. Also note that this will
+ # return 0 if the stack is empty, indicating a (putative) complete and
+ # non-corrupt line.
+ while bracket_stack:
+ line_score = line_score * 5 + \
+ score_bracket(match_bracket(bracket_stack.pop()))
+
+ return line_score
+
+def filter_zeros(scores):
+ """Remove zeros from the list of scores"""
+ return [s for s in scores if s != 0]
+
+def middle_score(scores):
+ """Sort and return the middle item of the list"""
+ # I could use `median` from numpy, but since the puzzle prompt promises an
+ # odd number of lines, it's easy to implement ourselves
+ return sorted(scores)[len(scores)//2]
+
+def solve_puzzle(input_string):
+ """Return the numeric solution to the puzzle"""
+ return middle_score(
+ filter_zeros([score_line(l) for l in convert_input_to_list(input_string)])
+ )
+
+def main():
+ """Run when the file is called as a script"""
+ assert solve_puzzle(EXAMPLE_INPUT) == 288957
+ print("Middle score of incomplete lines:",
+ solve_puzzle(get_puzzle_input(10)))
+
+if __name__ == "__main__":
+ main()
