1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
|
#!/bin/env python
L = [list(l.strip()) for l in open("input").readlines()]
UP = 0
RIGHT = 1
DOWN = 2
LEFT = 3
YLEN = len(L)
XLEN = len(L[0])
def put(y, x, c):
L[y][x] = c
def get(y, x):
if 0 <= y < YLEN and 0 <= x < XLEN:
return L[y][x]
return "#"
def start():
for y, row in enumerate(L):
for x, col in enumerate(row):
if col == "^":
L[y][x] = "."
return y, x
def move(y, x, d):
if d == UP and get(y - 1, x) == ".":
return (y - 1, x, UP)
if d == RIGHT and get(y, x + 1) == ".":
return (y, x + 1, RIGHT)
if d == DOWN and get(y + 1, x) == ".":
return (y + 1, x, DOWN)
if d == LEFT and get(y, x - 1) == ".":
return (y, x - 1, LEFT)
# else: rotate right
return (y, x, (d + 1) % 4)
def outside(y, x, d):
return (
(d == UP and y == 0)
or (d == RIGHT and x == XLEN - 1)
or (d == DOWN and y == YLEN - 1)
or (d == LEFT and x == 0)
)
def part1(y, x):
visits = set()
visits.add((y, x))
p = (y, x, UP)
while not outside(*p):
p = move(*p)
visits.add((p[0], p[1]))
print(len(visits))
def part2(ys, xs):
res = 0
def loopy(y, x):
visits = set()
p = (y, x, UP)
while not outside(*p):
if p in visits:
return True
visits.add(p)
p = move(*p)
return False
for y in range(YLEN):
for x in range(XLEN):
if get(y, x) == ".":
put(y, x, "#")
loops = loopy(ys, xs)
put(y, x, ".")
if loops:
res += 1
print(res)
s = start()
part1(*s)
part2(*s)
|
