From 9485fbae1dee52e252bfc6fcb19373b861b2f35a Mon Sep 17 00:00:00 2001
From: felixm <mail@felixm.de>
Date: Sat, 9 Dec 2023 11:48:39 -0500
Subject: [PATCH] Solve day 9 and fix horrible bug in lib.

My integer parser did not consider negative values. I have fixed that
in the 2022 repository, but not here. That's pretty annoying.
---
 README.md |  3 ++-
 d9.py     | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 lib.py    |  4 ++--
 3 files changed, 57 insertions(+), 3 deletions(-)
 create mode 100644 d9.py

diff --git a/README.md b/README.md
index ad7887d..b239c3c 100644
--- a/README.md
+++ b/README.md
@@ -7,4 +7,5 @@
 - Day 5: 1st 25:00, 2nd 1:55:00; Required patience and accuracy
 - Day 6: 13:54; I was slow because I thought it is much harder?
 - Day 7: 75:00; leaderboard 16:00... that was just bad; no excuse
-- Day 8:
+- Day 8: 57:00; my input parse function did not consider negative values...
+- Day 9:
diff --git a/d9.py b/d9.py
new file mode 100644
index 0000000..dadaebe
--- /dev/null
+++ b/d9.py
@@ -0,0 +1,53 @@
+import lib
+
+EXAMPLE = """
+0 3 6 9 12 15
+1 3 6 10 15 21
+10 13 16 21 30 45
+"""
+
+def solve(lines: list[str]):
+    res = 0
+    for (i, line) in enumerate(lines):
+        digits = lib.str_to_int_list(line)
+        last_digits = []
+        while not all(d == 0 for d in digits):
+            last_digits.append(digits[-1])
+            digits = [digits[i + 1] - digits[i] for i in range(len(digits) - 1)]
+        s = 0
+        for d in reversed(last_digits):
+            s = s + d
+        res += s
+    # 50:00 ... problem in my helper function... lol
+    return res
+
+def solve2(lines: list[str]):
+    res = 0
+    for (i, line) in enumerate(lines):
+        digits = lib.str_to_int_list(line)
+        first_digits = []
+        while not all(d == 0 for d in digits):
+            first_digits.append(digits[0])
+            digits = [digits[i + 1] - digits[i] for i in range(len(digits) - 1)]
+        s = 0
+        for d in reversed(first_digits):
+            s = d - s
+        res += s
+    # 57:00...
+    return res
+
+def main():
+    lines = lib.str_to_lines_no_empty(EXAMPLE)
+    print("Example  1:", solve(lines))
+
+    lines = lib.str_to_lines_no_empty(open("i9.txt").read())
+    print("Solution 1:", solve(lines))
+
+    lines = lib.str_to_lines_no_empty(EXAMPLE)
+    print("Example  2:", solve2(lines))
+
+    lines = lib.str_to_lines_no_empty(open("i9.txt").read())
+    print("Solution 2:", solve2(lines))
+
+if __name__ == "__main__":
+    main()
diff --git a/lib.py b/lib.py
index 2170f46..6373b11 100644
--- a/lib.py
+++ b/lib.py
@@ -34,13 +34,13 @@ def lcm(numbers: list[int]) -> int:
 
 def str_to_single_int(line: str) -> int:
     line = line.replace(" ", "")
-    r = re.compile(r"\d+")
+    r = re.compile(r"-?\d+")
     for m in r.findall(line):
         return int(m)
     raise Exception("No single digit sequence in '{line}'")
 
 def str_to_int_list(line: str) -> list[int]:
-    r = re.compile(r"\d+")
+    r = re.compile(r"-?\d+")
     return list(map(int, r.findall(line)))
 
 def str_to_lines_no_empty(text: str) -> list[str]: