From 4e97f88f70c4f1920e81f380ae9dedcb2b17e5e0 Mon Sep 17 00:00:00 2001
From: trwnh <a@trwnh.com>
Date: Tue, 15 Dec 2020 01:02:52 -0600
Subject: [PATCH] almost fell into a trap there

---
 2020/15/15.py     | 48 +++++++++++++++++++++++++++++++++++++++++++++++
 2020/15/input.txt |  1 +
 2 files changed, 49 insertions(+)
 create mode 100644 2020/15/15.py
 create mode 100644 2020/15/input.txt

diff --git a/2020/15/15.py b/2020/15/15.py
new file mode 100644
index 0000000..c966032
--- /dev/null
+++ b/2020/15/15.py
@@ -0,0 +1,48 @@
+def read_file():
+	with open("input.txt","r") as f:
+		return [int(x) for x in f.read().split(',')]
+
+def numbers_spoken(seed, limit):
+	"""Stores all numbers spoken."""
+	numbers = seed
+	i = len(seed)
+	number = seed[-1]
+	while len(numbers) != limit:
+		past = numbers[:-1]
+		if number not in past:
+			numbers.append(0)
+			number = 0
+		else:
+			last_spoken = len(past) + 1
+			most_recently_spoken = (len(past) - past[::-1].index(number))
+			turns_ago = last_spoken - most_recently_spoken
+			numbers.append(turns_ago)
+			number = turns_ago
+	return numbers[-1]
+
+def part1(seed):
+	return numbers_spoken(seed,2020)
+
+def number_spoken_on_turn(seed, turn):
+	"""Only cares about specific turn."""
+	last_spoken = {last: i+1 for i, last in enumerate(seed)}
+	number = seed[-1]
+	for i in range(len(seed),turn):
+		if number not in last_spoken:
+			last_spoken[number] = i
+			number = 0
+		else:
+			last = last_spoken[number]
+			last_spoken[number] = i
+			number = last_spoken[number] - last
+	return(number)
+
+def part2(seed):
+	return number_spoken_on_turn(seed,30000000)
+
+def main():
+	seed = read_file()
+	print(part1(seed), part2(seed))
+
+if __name__ == "__main__":
+	main()
\ No newline at end of file
diff --git a/2020/15/input.txt b/2020/15/input.txt
new file mode 100644
index 0000000..c184552
--- /dev/null
+++ b/2020/15/input.txt
@@ -0,0 +1 @@
+1,12,0,20,8,16
\ No newline at end of file