Add day 21 solution

day-21/day-21.py

@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+from pathlib import Path
+from collections import defaultdict
+
+
+def quantum_roll(state, p0, p1, s0, s1):
+    if s0 >= 21:
+        return (1, 0)
+    if s1 >= 21:
+        return (0, 1)
+    if (p0, p1, s0, s1) in state:
+        return state[(p0, p1, s0, s1)]
+    res = (0, 0)
+    for d0 in [1, 2, 3]:
+        for d1 in [1, 2, 3]:
+            for d2 in [1, 2, 3]:
+                new_p0 = (p0 + d0 + d1 + d2) % 10
+                new_s0 = s0 + new_p0 + 1
+                (x1, y1) = quantum_roll(state, p1, new_p0, s1, new_s0)
+                res = (res[0] + y1, res[1] + x1)
+    state[(p0, p1, s0, s1)] = res
+    return res
+
+
+def part_1(input):
+    result = 0
+    pos = []
+    pos.append(int(input[0].rstrip().split()[-1]) - 1)
+    pos.append(int(input[1].rstrip().split()[-1]) - 1)
+    score = [0, 0]
+    p = 0
+    dice = 1
+    while True:
+        pos[p] += sum(range(dice, dice + 3))
+        pos[p] %= 10
+        score[p] += pos[p] + 1
+        dice += 3
+        if 1000 <= score[p]:
+            p += 1
+            p %= 2
+            break
+        p += 1
+        p %= 2
+    result = score[p] * (dice - 1)
+    print("Part 1 result:", result)
+
+
+def part_2(input):
+    result = 0
+    state = {}
+    p0 = int(input[0].rstrip().split()[-1]) - 1
+    p1 = int(input[1].rstrip().split()[-1]) - 1
+    result = max(quantum_roll(state, p0, p1, 0, 0))
+    print("Part 2 result:", result)
+
+
+input = list()
+p = Path(__file__).with_name('input.txt')
+with open(p) as f:
+    input = f.readlines()
+    part_1(input)
+    part_2(input)

day-21/input.txt

@@ -0,0 +1,2 @@
+Player 1 starting position: 4
+Player 2 starting position: 10