Solution to day 21. A little late.

day-21/solution.py

@@ -0,0 +1,50 @@
+from __future__ import print_function, division
+from itertools import product, combinations
+import math
+
+def price(c):
+    return c[0][0] + c[1][0] + c[2][0][0] + c[2][1][0]
+
+def power(c):
+    return c[0][1] + c[1][1] + c[2][0][1] + c[2][1][1]
+
+def armor(c):
+    return c[0][2] + c[1][2] + c[2][0][2] + c[2][1][2]
+
+def wins(c, monsterHP, monsterAttack, monsterArmor):
+    monsterDamage = max(1, monsterAttack - armor(c))
+    heroDamage = max(1, power(c) - monsterArmor)
+
+    return math.ceil(100 / monsterDamage) >= math.ceil(monsterHP / heroDamage)
+
+weapons = [
+        (8, 4, 0),
+        (10, 5, 0),
+        (25, 6, 0),
+        (40, 7, 0),
+        (74, 8, 0)
+        ]
+
+armors = [
+        (0, 0, 0), # Dummy armor
+        (13, 0, 1),
+        (31, 0, 2),
+        (53, 0, 3),
+        (75, 0, 4),
+        (102, 0, 5)
+        ]
+
+rings = list(combinations([
+        (0, 0, 0), # Dummy ring
+        (0, 0, 0), # Second dummy ring
+        (25, 1, 0),
+        (50, 2, 0),
+        (100, 3, 0),
+        (20, 0, 1),
+        (40, 0, 2),
+        (80, 0, 3),
+        ], 2))
+
+
+print(min(price(c) for c in product(weapons, armors, rings) if wins(c, 103, 9, 2)))
+print(max(price(c) for c in product(weapons, armors, rings) if not wins(c, 103, 9, 2)))