2020 day1/python: modify for part2

2020/day1/day1.py

@@ -1,15 +1,22 @@
 #!/usr/bin/env python
+import itertools
 import sys
 from typing import Iterable
 
-def find2020(nums: Iterable[int]) -> int:
-    candidates = set()
+def product(nums: Iterable[int]) -> int:
+    """
+    Returns the product of all elements in 'nums'
+    """
+    x = 1
     for num in nums:
-        opposite = 2020-num
-        if num in candidates:
-            return num * opposite
-        candidates.add(opposite)
+        x *= num
+    return x
+
+def find_summing(arity: int, nums: Iterable[int]) -> int:
+    return product(next(filter(lambda xs: sum(xs) == 2020, itertools.permutations(nums, r=arity))))
 
 if __name__ == '__main__':
     with open(sys.argv[1], 'r') as f:
-        print(find2020(int(n) for n in f.readlines()))
+        nums = [int(n) for n in f.readlines()]
+    print(find_summing(2, nums))
+    print(find_summing(3, nums))