day9

Author: shuckc

2023/day9.py

@@ -0,0 +1,46 @@
+from common import ai
+import re
+import itertools
+from collections import defaultdict
+import math
+
+inp = """
+0 3 6 9 12 15
+1 3 6 10 15 21
+10 13 16 21 30 45
+"""
+def parse(inp):
+	for l in inp.strip().split("\n"):
+		yield list(map(int, l.split(" ")))
+
+def deltas(row):
+	return [r2-r1 for r1,r2 in zip(row[:-1], row[1:])]
+
+ai(deltas([0,3,6,9]), [3, 3, 3])
+
+def p1(inp):
+	t, t2 = 0, 0
+	for seq in parse(inp):
+		print(seq)
+		dd = seq
+		lasts = []
+		firsts = []
+		while True:
+			lasts.append(dd[-1])
+			firsts.append(dd[0])
+			dd = deltas(dd)
+			print(f"   {dd}")
+			if all([d == 0 for d in dd]):
+				nxt = sum(lasts)
+				prev = firsts[-1]
+				# p = f0 - (f1 - f2)
+				for f in reversed(firsts[:-1]):
+					prev = f - prev
+				print(f" {lasts} {firsts} next {nxt} prev {prev}")
+				t += nxt
+				t2 += prev
+				break
+	return t, t2
+
+ai(p1(inp), (114, 2))
+ai(p1(open("day9.txt").read()), (2038472161, 1091))