From 25b35e8f5c9f23278b495a8234afb26bf31b7afa Mon Sep 17 00:00:00 2001
From: a <a@trwnh.com>
Date: Sun, 13 Dec 2020 01:13:19 -0600
Subject: [PATCH] ughhhh

---
 2020/13/13.py            | 55 ++++++++++++++++++++++++++++++++++++++++
 2020/13/input.txt        |  2 ++
 2020/13/input_sample.txt |  2 ++
 3 files changed, 59 insertions(+)
 create mode 100644 2020/13/13.py
 create mode 100644 2020/13/input.txt
 create mode 100644 2020/13/input_sample.txt

diff --git a/2020/13/13.py b/2020/13/13.py
new file mode 100644
index 0000000..fa1d2a6
--- /dev/null
+++ b/2020/13/13.py
@@ -0,0 +1,55 @@
+def read_file():
+	with open("input.txt","r") as f:
+		timestamp, buses = f.read().split('\n')
+		timestamp = int(timestamp)
+		buses = buses.split(',')
+		working_buses = [int(b) for b in buses if b != "x"]
+		return timestamp, working_buses, buses
+
+def part1(timestamp, buses):
+	waits = [abs((timestamp % b) - b) for b in buses]
+	i = waits.index(min(waits))
+	return buses[i] * (waits[i])
+
+from functools import reduce
+def crt(a,n):
+	sum=0
+	product =reduce(lambda a, b: a*b, n)
+	for n_i, a_i in zip(n,a):
+		p = product // n_i
+		sum += a_i * mul_inv(p, n_i) * p
+	return sum % product
+def mul_inv(a, b):
+	b0 = b
+	x0, x1 = 0, 1
+	if b == 1:
+		return 1
+	while a > 1:
+		q = a // b
+		a, b = b, (a % b)
+		x0, x1 = (x1 - q * x0), x0
+	if x1 < 0:
+		x1 += b0
+	return x1
+
+def part2(buses):
+	r = []
+	m = []
+	for i, b in enumerate(buses): # i = wait, b = modulo
+		if b == "x":
+			continue
+		b = int(b)
+		r.append(b-i) # convert to remainder
+		m.append(b)
+	return crt(r,m)
+
+def main():
+	timestamp, working_buses, all_buses = read_file()
+	print(part1(timestamp, working_buses), part2(all_buses))
+	print(part2([17,"x",13,19])) # 3417
+	print(part2([67,7,59,61])) # 754018
+	print(part2([67,"x",7,59,61])) # 779210
+	print(part2([67,7,"x",59,61])) # 1261476
+	print(part2([1789,37,47,1889])) # 1202161486
+if __name__ == "__main__":
+	main()
\ No newline at end of file
diff --git a/2020/13/input.txt b/2020/13/input.txt
new file mode 100644
index 0000000..1f1ba00
--- /dev/null
+++ b/2020/13/input.txt
@@ -0,0 +1,2 @@
+1000417
+23,x,x,x,x,x,x,x,x,x,x,x,x,41,x,x,x,37,x,x,x,x,x,479,x,x,x,x,x,x,x,x,x,x,x,x,13,x,x,x,17,x,x,x,x,x,x,x,x,x,x,x,29,x,373,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,x,19
\ No newline at end of file
diff --git a/2020/13/input_sample.txt b/2020/13/input_sample.txt
new file mode 100644
index 0000000..e473080
--- /dev/null
+++ b/2020/13/input_sample.txt
@@ -0,0 +1,2 @@
+939
+7,13,x,x,59,x,31,19
\ No newline at end of file