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Solve 2019 day 23

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felixm
2024-10-11 22:01:40 -04:00
parent df31b47934
commit 67914a642a
3 changed files with 60 additions and 12 deletions
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22
2019/d22.py
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@@ -9,12 +9,12 @@ for line in data.splitlines():
if "new stack" in line:
deck = list(reversed(deck))
elif "cut" in line:
n, = str_to_ints(line)
(n,) = str_to_ints(line)
deck = deck[n:] + deck[:n]
elif "increment" in line:
new_deck = [-1] * len(deck)
pos = 0
n, = str_to_ints(line)
(n,) = str_to_ints(line)
deck = list(reversed(deck))
while deck:
new_deck[pos] = deck.pop()
@@ -37,7 +37,7 @@ for line in data.splitlines():
assert rev_index == index
index = new_index
elif "cut" in line:
cut, = str_to_ints(line)
(cut,) = str_to_ints(line)
cut = (len + cut) % len
if index >= cut:
new_index = index - cut
@@ -48,7 +48,7 @@ for line in data.splitlines():
index = new_index
# calculate index from new_index and store in rev_index
elif "increment" in line:
n, = str_to_ints(line)
(n,) = str_to_ints(line)
assert gcd(n, len) == 1
new_index = (n * index) % len
m = mod_inverse(n, len)
@@ -63,11 +63,11 @@ for line in reversed(data.splitlines()):
if "new stack" in line:
index = -(index - len + 1)
elif "cut" in line:
cut, = str_to_ints(line)
(cut,) = str_to_ints(line)
cut = (len + cut) % len
index = (index + cut) % len
elif "increment" in line:
n, = str_to_ints(line)
(n,) = str_to_ints(line)
assert gcd(n, len) == 1
m = mod_inverse(n, len)
index = (index * m) % len
@@ -80,6 +80,7 @@ len = 119315717514047
# get expression for one loop using sympy
from sympy import symbols, simplify
index = symbols("index")
expr = index
for line in lines:
@@ -87,16 +88,16 @@ for line in lines:
# index = -(index - len + 1)
expr = -(expr - len + 1)
elif "cut" in line:
cut, = str_to_ints(line)
(cut,) = str_to_ints(line)
cut = (len + cut) % len
# index = (index + cut) % len
expr = (expr + cut)
expr = expr + cut
elif "increment" in line:
n, = str_to_ints(line)
(n,) = str_to_ints(line)
assert gcd(n, len) == 1
m = mod_inverse(n, len)
# index = (index * m) % len
expr = (expr * m)
expr = expr * m
# we can see that expression is in the form (a - b * i) % m
expr = simplify(expr % len)
@@ -115,4 +116,3 @@ term1 = (p_t * r0) % m
term2 = (a * (1 - p_t) * inv_b1) % m
r_t = (term1 + term2) % m
print(r_t)