day21.py

day21.py

def mod1(num,m): return num % m or m
cache = {}

def play_round(player,pos1,score1,pos2,score2):
  if (pos1,score1,pos2,score2) in cache:
    return cache[(pos1,score1,pos2,score2)]
  # swap 0/1 below to get the other player wins
  if score1 >= 21:
    return 1
  if score2 >= 21:
    return 0
  wins = 0
  for roll in itertools.product([1,2,3],repeat=3):
    r = sum(roll)
    if player == 1:        
      new_pos = points = mod1(pos1 + r,10)
      wins += play_round(2,new_pos,score1+points,pos2,score2)
    else:
      new_pos = points = mod1(pos2 + r,10)
      wins += play_round(1,pos1,score1,new_pos,score2+points)
  cache[(pos1,score1,pos2,score2)] = wins
  return wins