1 files changed, 137 insertions, 0 deletions
diff --git a/22/main.py b/22/main.py
new file mode 100755
index 0000000..9b7bb0b
--- /dev/null
+++ b/22/main.py
@@ -0,0 +1,137 @@
+#!/usr/bin/python
+
+from copy   import copy
+from random import randrange
+
+
+
+class Entity:
+    pass
+
+
+
+def solve_partn(partn, player_stats, boss_stats):
+    # We assign numbers 0-4 to the spells
+    mana_costs = [53, 73, 113, 173, 229]
+
+    least_mana = 666666
+    # 100K attempts turns out to be enough to reliably find the solution
+    for i in range(100000):
+        boss   = copy(  boss_stats)
+        player = copy(player_stats)
+
+        spent_mana = 0
+        # Timers for "Shield", "Poison" and "Recharge", respectively
+        timers = [0, 0, 0]
+
+        turn = 0
+        while boss.health > 0 and player.health > 0:
+            # Already spent too much; this can't be the solution, abort
+            if spent_mana > least_mana:
+                break
+
+            # Part 2: hard mode: player loses 1 HP at start of their turn
+            if partn == 2 and turn % 2 == 0:
+                player.health -= 1
+                if player.health <= 0:
+                    break
+
+            # Apply status effects from past spells
+            # "Shield"
+            if timers[0] > 0:
+                timers[0] -= 1
+                if timers[0] == 0:
+                    player.armour -= 7
+            # "Poison"
+            if timers[1] > 0:
+                boss.health -= 3
+                # Did the boss die before any actions were taken?
+                if boss.health <= 0:
+                    break
+                timers[1] -= 1
+            # "Recharge"
+            if timers[2] > 0:
+                player.mana += 101
+                timers[2] -= 1
+
+            # Player's turn to cast a spell
+            if turn % 2 == 0:
+                # Can we afford to cast any spell? If not, we've lost; abort
+                if player.mana < min(mana_costs):
+                    break
+
+                # Randomly select which spell to cast. Sounds inefficient, but
+                # works fine: we want to minimize the total mana spent, so we're
+                # looking for short sequences, which we're very unlikely to miss.
+                s = -1
+                while s == -1:
+                    s = randrange(0, 5)
+                    # Can we afford this spell?
+                    if mana_costs[s] > player.mana:
+                        s = -1
+                    # Isn't this spell already active?
+                    if s in [2, 3, 4] and timers[s - 2] > 0:
+                        s = -1
+
+                player.mana -= mana_costs[s]
+                spent_mana  += mana_costs[s]
+
+                # Apply effect of the spell we've selected
+                # "Magic Missile"
+                if s == 0:
+                    boss.health -= 4
+                # "Drain"
+                if s == 1:
+                    boss.health   -= 2
+                    player.health += 2
+                # "Shield"
+                if s == 2:
+                    timers[0] = 6
+                    player.armour += 7
+                # "Poison"
+                if s == 3:
+                    timers[1] = 6
+                # "Recharge"
+                if s == 4:
+                    timers[2] = 5
+
+            # Boss' turn to attack
+            else: # turn % 2 == 1
+                player.health -= max(1, boss.damage - player.armour)
+
+            turn += 1
+
+        # Did we stop because the player won?
+        if boss.health <= 0:
+            if spent_mana < least_mana:
+                least_mana = spent_mana
+
+    return least_mana
+
+
+
+def main():
+    # Set up player's stats given in puzzle text
+    player = Entity()
+    player.health =  50
+    player.armour =   0
+    player.mana   = 500
+
+    # Read boss' stats from input text file
+    boss = Entity()
+    with open("input.txt", "r") as f:
+        lines = f.read().splitlines()
+        for i in range(len(lines)): # len(lines) = 2
+            words = lines[i].split()
+            if i == 0:
+                boss.health = int(words[-1])
+            if i == 1:
+                boss.damage = int(words[-1])
+
+    print("Part 1 solution:", solve_partn(1, player, boss)) # 1269 for me
+    print("Part 2 solution:", solve_partn(2, player, boss)) # 1309 for me
+
+
+
+if __name__ == "__main__":
+    main()