My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Update 2016/day15.py
Add numerical solution using Chinese remainder theorem.
+32
-3
+32
-3
2016/day15.py
+32
-3
2016/day15.py
···
1
1
import re
2
2
import fileinput
3
-
from utils import parse_line
3
+
from utils import parse_line, mul
4
4
5
5
6
6
def button_timing(discs):
···
20
20
21
21
i += stride
22
22
23
+
# https://stackoverflow.com/a/9758173/239076
24
+
def egcd(a, b):
25
+
if a == 0:
26
+
return (b, 0, 1)
27
+
else:
28
+
g, y, x = egcd(b % a, a)
29
+
return (g, x - (b // a) * y, y)
30
+
31
+
def modinv(a, m):
32
+
g, x, y = egcd(a, m)
33
+
if g != 1:
34
+
raise Exception('modular inverse does not exist')
35
+
else:
36
+
return x % m
37
+
38
+
def chinese_remainder_theorem(discs):
39
+
M = mul(d[0] for d in discs)
40
+
x = 0
41
+
42
+
for i, (size, initial) in enumerate(discs, start=1):
43
+
# Disc #2 has 17 positions; at time=0, it is at position 15.
44
+
# => x \equiv (17 - 15 - 2) (mod 17)
45
+
M_i = (M / size)
46
+
x += (size - initial - i) * M_i * modinv(M_i, size)
47
+
48
+
return x
49
+
23
50
24
51
DISCS = []
25
52
DISC_RE = re.compile(r'Disc #\d+ has (\d+) positions; at time=0, it is at position (\d+).')
···
28
55
disc = parse_line(DISC_RE, line.strip())
29
56
DISCS.append(disc)
30
57
31
-
print "Timing to press button:", button_timing(DISCS)
32
-
print "Timing with added disc:", button_timing(DISCS + [[11, 0]])
58
+
# print "Timing to press button:", button_timing(DISCS)
59
+
# print "Timing with added disc:", button_timing(DISCS + [[11, 0]])
60
+
print "Timing to press button:", chinese_remainder_theorem(DISCS)
61
+
print "Timing with added disc:", chinese_remainder_theorem(DISCS + [[11, 0]])