My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add 2021/21
+101
+101
2021/day21.py
+101
2021/day21.py
···
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import fileinput
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from collections import Counter
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from itertools import product
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from utils import parse_nums
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# Read problem input.
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start_pos = {}
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for line in fileinput.input():
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nums = parse_nums(line)
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start_pos[nums[0]] = nums[1]
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# Solve part 1.
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curr_die = 1
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total_rolls = 0
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p1_score = 0
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p2_score = 0
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p1 = start_pos[1]
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p2 = start_pos[2]
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while p1_score < 1000 and p2_score < 1000:
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p1 -= 1
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for i in range(3):
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total_rolls += 1
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p1 += curr_die
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curr_die += 1
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if curr_die == 101:
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curr_die = 1
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p1 = p1 % 10
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p1 += 1
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p1_score += p1
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if p1_score >= 1000:
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break
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p2 -= 1
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for i in range(3):
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total_rolls += 1
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p2 += curr_die
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curr_die += 1
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if curr_die == 101:
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curr_die = 1
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p2 = p2 % 10
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p2 += 1
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p2_score += p2
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print "Part 1:", total_rolls * min(p1_score, p2_score)
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# Solve part 2.
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# All possible roll totals of the quantum dice for a given turn.
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rolls = [sum(p) for p in product([1, 2, 3], repeat=3)]
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p1 = start_pos[1]
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p2 = start_pos[2]
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# Each universe is represented by (p1_pos, p2_pos, p1_score, p2_score).
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universes = Counter([(p1, p2, 0, 0)])
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while not all(s1 >= 21 or s2 >= 21 for p1, p2, s1, s2 in universes):
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next_universes = Counter()
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for (p1, p2, s1, s2), count in universes.items():
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if s1 >= 21 or s2 >= 21:
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next_universes[p1, p2, s1, s2] += count
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continue
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for r in rolls:
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np = (((p1 + r) - 1) % 10) + 1
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next_universes[(np, p2, s1 + np, s2)] += count
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universes = next_universes
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next_universes = Counter()
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for (p1, p2, s1, s2), count in universes.items():
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if s1 >= 21 or s2 >= 21:
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next_universes[p1, p2, s1, s2] += count
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continue
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for r in rolls:
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np = (((p2 + r) - 1) % 10) + 1
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next_universes[(p1, np, s1, s2 + np)] += count
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universes = next_universes
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p1_wins = 0
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p2_wins = 0
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for (p1, p2, s1, s2), v in universes.items():
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if s1 >= 21:
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p1_wins += v
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else:
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p2_wins += v
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print "Part 2:", max(p1_wins, p2_wins)