StyleInCode

""" day_16_01.py """

# usage: python3 day_16_01.py < input

import sys
from collections import deque
from collections import namedtuple


Point = namedtuple('GridPoint', 'x, y')


def ingest():
    """ parse standard input """
    def find(item):
        """ where is it """
        return [p for p, i in plan.items() if i == item][0]

    plan = {}
    x, y = 0, 0
    with sys.stdin as infile:
        for item in infile.read():
            if item == '\n':
                x, y = 0, y + 1
            else:
                plan[Point(x, y)] = item
                x = x + 1

    return find('S'), find('E'), plan


def route_scores(start, stop, plan):
    """ calculate route scores through plan """
    def adjacent(square, aim, tally):
        """ adjacent squares """
        output = set()
        for dx, dy in [(0, -1), (1, 0), (0, 1), (-1, 0)]:
            p = Point(square.x + dx, square.y + dy)
            if plan.get(p, '#') != '#':
                penalty = 1 if aim == (dx, dy) else 1001
                output.add((p, (dx, dy), tally + penalty))

        return output

    scores = []
    explore = deque([(start, (1, 0), 0)])
    visited = {}
    while explore:
        tile, way, score = explore.popleft()
        if tile == stop:
            scores.append(score)
        else:
            tws = []
            for t, w, s in adjacent(tile, way, score):
                if visited.get((t, w), s) >= s:
                    visited[(t, w)] = s
                    tws.append((t, w, s))
            explore.extend(tws)

    return scores


begin, end, maze = ingest()
lowest_score = min(route_scores(begin, end, maze))

print(lowest_score)