2023: d09: ex2: add solution

2023/d09/ex2/ex2.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+
+
+def solve(input: list[str]) -> int:
+    def parse_line(line: str) -> list[int]:
+        return [int(n) for n in line.split()]
+
+    def parse(input: list[str]) -> list[list[int]]:
+        return [parse_line(line) for line in input]
+
+    def extrapolate(sequence: list[int]) -> int:
+        diffs = [n - p for p, n in itertools.pairwise(sequence)]
+        if all(n == 0 for n in diffs):
+            return sequence[-1]
+        return sequence[-1] + extrapolate(diffs)
+
+    sequences = parse(input)
+
+    return sum(extrapolate(seq[::-1]) for seq in sequences)
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()