10.py

map: [[int]] = []

with open('input.txt', 'r') as file:
    for line in file:
        map_row = []
        for char in line.strip():
            map_row.append(int(char))
        map.append(map_row)

def solve_part1():
    def walk_trail(x: int, y: int, end_positions: set[tuple[int, int]]) -> int:
        height = map[y][x]
        if height == 9:
            end_positions.add((x, y))
            return

        # left
        if x > 0 and map[y][x - 1] == height + 1:
            walk_trail(x - 1, y, end_positions)
        # up
        if y > 0 and map[y - 1][x] == height + 1:
            walk_trail(x, y - 1, end_positions)
        # right
        if x < len(map[y]) - 1 and map[y][x + 1] == height + 1:
            walk_trail(x + 1, y, end_positions)
        # down
        if y < len(map) - 1 and map[y + 1][x] == height + 1:
            walk_trail(x, y + 1, end_positions)

    total_score = 0
    for y in range(len(map)):
        for x in range(len(map[y])):
            if map[y][x] == 0:
                end_positions = set()
                walk_trail(x, y, end_positions)
                total_score += len(end_positions)

    print('Sum of scores for all trailheads (part 1):', total_score)

def solve_part2():
    def walk_trail(x, y) -> int:
        height = map[y][x]
        if height == 9:
            return 1

        score = 0
        # left
        if x > 0 and map[y][x - 1] == height + 1:
            score += walk_trail(x - 1, y)
        # up
        if y > 0 and map[y - 1][x] == height + 1:
            score += walk_trail(x, y - 1)
        # right
        if x < len(map[y]) - 1 and map[y][x + 1] == height + 1:
            score += walk_trail(x + 1, y)
        # down
        if y < len(map) - 1 and map[y + 1][x] == height + 1:
            score += walk_trail(x, y + 1)
        return score

    total_score = 0
    for y in range(len(map)):
        for x in range(len(map[y])):
            if map[y][x] == 0:
                total_score += walk_trail(x, y)

    print('Sum of ratings for all trailheads (part 2):', total_score)

solve_part1()
solve_part2()