Day 3

day3_part1.py

#!/usr/bin/env python3

from typing import List, Tuple

LEFT_RIGHT_DIRECTIONS = tuple(range(-1, 2))
CENTRAL_DIRECTIONS = tuple(i for i in range(-1, 2) if i != 0)

with open("input.txt", "r") as f:
    matrix = [line.strip() for line in f]

n, m = len(matrix), len(matrix[0])
total_sum = 0

def find_the_symbol(i: int, j: int, n: int, matrix: List[str], directions: Tuple[int, ...]) -> bool:
    for di in directions:
        if 0 <= i + di < n and not matrix[i + di][j].isnumeric() and matrix[i + di][j] != ".":
            return True
    return False


for i in range(n):
    j = 0
    while j < m:
        if matrix[i][j].isnumeric():
            number = int(matrix[i][j])
            jj = j + 1
            has_symbols = False

            if j > 0:
                has_symbols = find_the_symbol(i, j - 1, n, matrix, LEFT_RIGHT_DIRECTIONS)
            if not has_symbols:
                has_symbols = find_the_symbol(i, j, n, matrix, CENTRAL_DIRECTIONS)
            while jj < m and matrix[i][jj].isnumeric():
                number = number * 10 + int(matrix[i][jj])
                if not has_symbols:
                    has_symbols = find_the_symbol(i, jj, n, matrix, CENTRAL_DIRECTIONS)
                jj += 1

            if not has_symbols and jj < m:
                has_symbols = find_the_symbol(i, jj, n, matrix, LEFT_RIGHT_DIRECTIONS)

            if has_symbols:
                total_sum += number

            j = jj
        else:
            j += 1

print(total_sum)

day3_part2.py

#!/usr/bin/env python3

from typing import List, Optional, Tuple

LEFT_RIGHT_DIRECTIONS = tuple(range(-1, 2))
CENTRAL_DIRECTIONS = tuple(i for i in range(-1, 2) if i != 0)
ALL_DIRECTIONS = tuple((i, j,) for i in range(-1, 2) for j in range(-1, 2) if i != 0 or j != 0)


with open("input.txt", "r") as f:
    matrix = [line.strip() for line in f]

n, m = len(matrix), len(matrix[0])
total_sum = 0

def find_gear_part(i: int, j: int, n: int, matrix: List[str], directions: Tuple[int, ...]) -> Optional[Tuple[int, int]]:
    for di in directions:
        if 0 <= i + di < n and matrix[i + di][j] == "*":
            return (i + di, j, )
    return None


for i in range(n):
    j = 0
    while j < m:
        if matrix[i][j].isnumeric():
            used = {(i, j, ), }
            number = int(matrix[i][j])
            jj = j + 1
            asterisk_coordinates = None

            if j > 0:
                asterisk_coordinates = find_gear_part(i, j - 1, n, matrix, LEFT_RIGHT_DIRECTIONS)
            if not asterisk_coordinates:
                asterisk_coordinates = find_gear_part(i, j, n, matrix, CENTRAL_DIRECTIONS)
            while jj < m and matrix[i][jj].isnumeric():
                used.add((i, jj, ))
                number = number * 10 + int(matrix[i][jj])
                if not asterisk_coordinates:
                    asterisk_coordinates = find_gear_part(i, jj, n, matrix, CENTRAL_DIRECTIONS)
                jj += 1

            if not asterisk_coordinates and jj < m:
                asterisk_coordinates = find_gear_part(i, jj, n, matrix, LEFT_RIGHT_DIRECTIONS)
            
            if asterisk_coordinates:
                number_position = None
                for di, dj in ALL_DIRECTIONS:
                    if 0 <= asterisk_coordinates[0] + di < n and \
                            0 <= asterisk_coordinates[1] + dj < m and \
                            not (asterisk_coordinates[0] + di, asterisk_coordinates[1] + dj, ) in used and \
                            matrix[asterisk_coordinates[0] + di][asterisk_coordinates[1] + dj].isnumeric():
                        number_position = (asterisk_coordinates[0] + di, asterisk_coordinates[1] + dj, )
                        break
                if number_position:
                    i2, j2 = number_position
                    while j2 > 0 and matrix[i2][j2 - 1].isnumeric():
                        j2 -= 1
                    new_number = int(matrix[i2][j2])
                    j2 += 1
                    while j2 < m and matrix[i2][j2].isnumeric():
                        new_number = new_number * 10 + int(matrix[i2][j2])
                        j2 += 1
                    total_sum += number * new_number
            j = jj
        else:
            j += 1

print(total_sum >> 1)