day 16

l = [list(x) for x in open('input').read().splitlines()]
dirs = {'>': (0, 1), '<': (0, -1), '^': (-1, 0), 'v': (1, 0)}
mirrors = {
    '/': {'>': ['^'], '<': ['v'], '^': ['>'], 'v': ['<']},
    '\\': {'>': ['v'], '<': ['^'], '^': ['<'], 'v': ['>']},
    '|': {'>': ['v', '^'], '<': ['v', '^'], '^': ['^'], 'v': ['v']},
    '-': {'>': ['>'], '<': ['<'], '^': ['>', '<'], 'v': ['>', '<']}}
mirrors['.'] = {i: [i] for i in dirs.keys()}
def energized(start=(0, 0, '>')):
    ene = set()
    stack = [start]
    while stack:
        x, y, dr = stack.pop()
        if (x, y, dr) in ene:
            continue
        ene.add((x, y, dr))
        for d in mirrors[l[x][y]][dr]:
            x, y = x + dirs[d][0], y + dirs[d][1]
            if x in range(len(l)) and y in range(len(l[0])):
                stack.append((x, y, d))
    return len(set((x, y) for x, y, _ in ene))

starts=[]
for x in range(len(l)):
    starts+=[(x, 0, '>'),(x, len(l[0]) - 1, '<')]
for y in range(len(l[0])):
    starts+=[(0, y, 'v'),(len(l) - 1, y, '^')]

print(f"Part 1: {energized()}")
print(f"Part 2: {max(energized(start) for start in starts)}")