day-10

Syntax Scoring

Content Decoding

The navigation subsystem syntax is made of several lines containing chunks.

The challenge offers the following hierarchy:

file > line > chunk

The corresponding decoding logic:

with open(filename, encoding='utf-8') as buffer:
    for line in buffer.readlines():
        chunks = line.strip()
        yield chunks

First Part

Starting from the end:

Find the first illegal character in each corrupted line of the navigation subsystem. What is the total syntax error score for those errors?

The corresponding high-level method:

def solve_first_part(contents: Generator) -> int:
    answer = 0
    for line in contents:
        for se in scan_syntax(line):
            answer += ERROR_SCORE[se]
            break
    return answer

The rest of the code consists in structure declarations.

Contents	Command	Answer	Time
input.txt	./day_10.py -p 1 input.txt	268845	0.5 ms

Second Part

Following on the work laid out prior, the second part requires discarding previously matched lines. This done by checking if the scan_syntax() method returned at least a single entry.

corrupted_line = any(True for _ in scan_syntax(line=line))
if corrupted_line:
    continue

The completion string is then built using a dedicated autocomplete() method:

def autocomplete(line: str) -> str:
    chunks = list()
    for chunk in line:
        opening_token = chunk in OPENING_MAP
        if opening_token:
            chunks.insert(0, OPENING_MAP[chunk])
        else:
            chunks.pop(0)
    return ''.join(chunks)

No grounds were broken here, although push / pop operations are done on the other side of the list which results in the reversed ordering of the remaining items.

The higher level solve_second_part() is also straight forward.

def solve_second_part(contents: Iterator[str]) -> int:
    scores = list()
    for line in contents:
        corrupted_line = any(True for _ in scan_syntax(line=line))
        if corrupted_line:
            continue
        completion_string = autocomplete(line=line)
        score = 0
        for char in completion_string:
            score = 5 * score + CLOSING_SCORE[char]
        scores.append(score)
    scores.sort()
    answer = scores[len(scores) // 2]
    return answer

Contents	Command	Answer	Time
input.txt	./day_10.py -p 2 input.txt	4038824534	0.9 ms