Solve 2019 day 22

2018/d24.py

@@ -0,0 +1,179 @@
+import re
+from lib import get_data, ints
+from collections import defaultdict
+from copy import deepcopy
+
+r = re.compile(r"(immune|weak) to ([\w ,]+)")
+r_strength = re.compile(r"(\w+) damage")
+
+data = """Immune System:
+17 units each with 5390 hit points (weak to radiation, bludgeoning) with an attack that does 4507 fire damage at initiative 2
+989 units each with 1274 hit points (immune to fire; weak to bludgeoning, slashing) with an attack that does 25 slashing damage at initiative 3
+
+Infection:
+801 units each with 4706 hit points (weak to radiation) with an attack that does 116 bludgeoning damage at initiative 1
+4485 units each with 2961 hit points (immune to radiation; weak to fire, cold) with an attack that does 12 slashing damage at initiative 4
+ """
+data = get_data(__file__)
+
+ARMY, ID, UNITS, HITS, DAMG, INIT = 0, 1, 2, 3, 4, 5
+
+groups = []
+unit_meta = {}
+
+id = 1
+for a, p in enumerate(data.split("\n\n")):
+    for line in p.splitlines():
+        xs = ints(line)
+        if len(xs) == 0:
+            continue
+        assert len(xs) == 4
+        xs = [a, id] + xs
+
+        (attack,) = r_strength.findall(line)
+        defense = defaultdict(list)
+        for attr, values in r.findall(line):
+            defense[attr] = values.split(", ")
+
+        unit_meta[id] = attack, defense
+        groups.append(xs)
+        id += 1
+
+
+def effective_power(group):
+    return (group[UNITS] * group[DAMG], group[INIT])
+
+
+def damage(g1, g2):
+    """Damage g1 does to g2"""
+    g1_id, g2_id = g1[ID], g2[ID]
+    g1_attack_type = unit_meta[g1_id][0]
+    g2_defenses = unit_meta[g2_id][1]
+    g2_immune = True if g1_attack_type in g2_defenses["immune"] else False
+    g2_weak = True if g1_attack_type in g2_defenses["weak"] else False
+
+    assert (g2_immune and g2_weak) != True
+
+    damage = g1[UNITS] * g1[DAMG]
+    if g2_immune:
+        damage = 0
+    elif g2_weak:
+        damage *= 2
+    return damage
+
+
+groups_orig = deepcopy(groups)
+while True:
+    groups = sorted(groups, key=effective_power, reverse=True)
+    attacks = {}
+    attacked = set()
+    for g in groups:
+        target_max_stats = 0, 0, 0
+        target = None
+        for t in groups:
+            if g[ARMY] == t[ARMY]:
+                continue
+            if g[ID] == t[ID]:
+                continue
+            if t[ID] in attacked:
+                continue
+            target_stats = damage(g, t), effective_power(t)[0], t[INIT]
+            if target_stats[0] == 0:
+                continue
+            if target_stats > target_max_stats:
+                target_max_stats = target_stats
+                target = t
+
+        if target is not None:
+            attacked.add(target[ID])
+            attacks[g[ID]] = target
+
+    groups = sorted(groups, key=lambda g: g[INIT], reverse=True)
+    for g in groups:
+        if g[ID] not in attacks:
+            continue
+        if g[UNITS] <= 0:
+            continue
+
+        target = attacks[g[ID]]
+        cdamage = damage(g, target)
+        units_dead = cdamage // target[HITS]
+        units_dead = units_dead if units_dead <= target[UNITS] else target[UNITS]
+        # print("immune" if g[ARMY] == 0 else "infection", g[ID], "attacks", target[ID], "dead", units_dead)
+        target[UNITS] -= units_dead
+
+    groups = [g for g in groups if g[UNITS] > 0]
+    armies = set()
+    for g in groups:
+        armies.add(g[ARMY])
+    assert len(armies) >= 1
+    if len(armies) == 1:
+        break
+
+
+t = sum(g[UNITS] for g in groups)
+print(t)
+
+
+for boost in range(0, 1800):
+    groups = deepcopy(groups_orig)
+    for g in groups:
+        if g[ARMY] == 0:
+            g[DAMG] += boost
+
+    while True:
+        groups = sorted(groups, key=effective_power, reverse=True)
+        attacks = {}
+        attacked = set()
+        for g in groups:
+            target_max_stats = 0, 0, 0
+            target = None
+            for t in groups:
+                if g[ARMY] == t[ARMY]:
+                    continue
+                if g[ID] == t[ID]:
+                    continue
+                if t[ID] in attacked:
+                    continue
+                target_stats = damage(g, t), effective_power(t)[0], t[INIT]
+                if target_stats[0] == 0:
+                    continue
+                if target_stats > target_max_stats:
+                    target_max_stats = target_stats
+                    target = t
+
+            if target is not None:
+                attacked.add(target[ID])
+                attacks[g[ID]] = target
+
+        groups = sorted(groups, key=lambda g: g[INIT], reverse=True)
+        max_dead = 0
+        for g in groups:
+            if g[ID] not in attacks:
+                continue
+            if g[UNITS] <= 0:
+                continue
+
+            target = attacks[g[ID]]
+            cdamage = damage(g, target)
+            units_dead = cdamage // target[HITS]
+            units_dead = units_dead if units_dead <= target[UNITS] else target[UNITS]
+            max_dead = max(units_dead, max_dead)
+            # print("immune" if g[ARMY] == 0 else "infection", g[ID], "attacks", target[ID], "dead", units_dead)
+            target[UNITS] -= units_dead
+
+        if max_dead == 0:
+            break
+
+        groups = [g for g in groups if g[UNITS] > 0]
+        armies = set()
+        for g in groups:
+            armies.add(g[ARMY])
+        assert len(armies) >= 1
+        if len(armies) == 1:
+            army = groups[0][ARMY]
+            t = sum(g[UNITS] for g in groups)
+            if army == 0:
+                print(t)
+                exit(0)
+            break

2018/d25.py

@@ -0,0 +1,38 @@
+from lib import get_data, ints
+
+
+def mdist(x, y):
+    return sum(abs(a - b) for a, b in zip(x, y))
+
+
+data = get_data(__file__)
+xss = [tuple(ints(line)) for line in data.splitlines()]
+
+# check if we can use set (even though we didn't end up using sets)
+assert len(xss) == len(set(xss))
+
+unplaced = list(xss)
+groups = [[unplaced.pop()]]
+while unplaced:
+    # see if any start fits into the current group
+    current_group = groups[-1]
+    add = None
+    for u in unplaced:
+        for x in current_group:
+            if mdist(u, x) <= 3:
+                add = u
+                break
+        if add is not None:
+            break
+
+    if add is not None:
+        # if yes, add the start to that group and see if another one can be
+        # added to the same group
+        unplaced.remove(add)
+        current_group.append(add)
+    else:
+        # if no, create a new group with an unplaced start
+        groups.append([unplaced.pop()])
+
+
+print(len(groups))

2019/d22.py

@@ -4,6 +4,7 @@ from math import gcd
 data = get_data(__file__)
 deck = list(range(10007))
 
+# part 1
 for line in data.splitlines():
     if "new stack" in line:
         deck = list(reversed(deck))
@@ -24,30 +25,94 @@ for line in data.splitlines():
 
 print(deck.index(2019))
 
-# idea: just follow the index of the target card
-len = 119315717514047
 len = 10007
-index = 2019
+orig_index = 2019
 
-
-for i in range(101741582076661):
-    for line in data.splitlines():
+# figure out how to reverse...
+index = orig_index
+for line in data.splitlines():
     if "new stack" in line:
-            index = len - (index + 1)
+        new_index = len - (index + 1)
+        rev_index = -(new_index - len + 1)
+        assert rev_index == index
+        index = new_index
     elif "cut" in line:
         cut, = str_to_ints(line)
         cut = (len + cut) % len
         if index >= cut:
-                index = index - cut
+            new_index = index - cut
         else:
-                index = (len - cut) + index
+            new_index = (len - cut) + index
+        rev_index = (new_index + cut) % len
+        assert rev_index == index
+        index = new_index
+        # calculate index from new_index and store in rev_index
     elif "increment" in line:
         n, = str_to_ints(line)
         assert gcd(n, len) == 1
         new_index = (n * index) % len
         m = mod_inverse(n, len)
-            assert (new_index * m) % len == index
+        rev_index = (new_index * m) % len
+        assert rev_index == index
         index = new_index
-    break
 
-print(index)
+assert index == deck.index(2019)
+
+# check that reverse approach works
+for line in reversed(data.splitlines()):
+    if "new stack" in line:
+        index = -(index - len + 1)
+    elif "cut" in line:
+        cut, = str_to_ints(line)
+        cut = (len + cut) % len
+        index = (index + cut) % len
+    elif "increment" in line:
+        n, = str_to_ints(line)
+        assert gcd(n, len) == 1
+        m = mod_inverse(n, len)
+        index = (index * m) % len
+assert index == orig_index
+
+lines = list(reversed(data.splitlines()))
+
+# new length of deck
+len = 119315717514047
+
+# get expression for one loop using sympy
+from sympy import symbols, simplify
+index = symbols("index")
+expr = index
+for line in lines:
+    if "new stack" in line:
+        # index = -(index - len + 1)
+        expr = -(expr - len + 1)
+    elif "cut" in line:
+        cut, = str_to_ints(line)
+        cut = (len + cut) % len
+        # index = (index + cut) % len
+        expr = (expr + cut)
+    elif "increment" in line:
+        n, = str_to_ints(line)
+        assert gcd(n, len) == 1
+        m = mod_inverse(n, len)
+        # index = (index * m) % len
+        expr = (expr * m)
+
+# we can see that expression is in the form (a - b * i) % m
+expr = simplify(expr % len)
+coeff_dict = expr.args[0].as_coefficients_dict()
+a = coeff_dict[1]
+b = -coeff_dict[index]
+
+# math
+n_shuffles = 101741582076661
+r0 = 2020
+m = len
+p = (-b) % m
+p_t = pow(p, n_shuffles, m)
+inv_b1 = mod_inverse(b + 1, m)
+term1 = (p_t * r0) % m
+term2 = (a * (1 - p_t) * inv_b1) % m
+r_t = (term1 + term2) % m
+print(r_t)
+

README.md

@@ -106,11 +106,13 @@ Solutions and utility script for Advent of Code challenges in Python.
 - Day 16: 36:10
 - Day 17: 180:00
 - Day 18: 24:04
-- Day 19: days, super fun, but hard for me
+- Day 19: days (super fun, but hard for me)
 - Day 20:
 - Day 21: 28:40 (16th - brute force but still not so bad)
 - Day 22: 185:00 (should not have been so slow but was fun)
-- Day 23:
+- Day 23: days
+- Day 24: days
+- Day 25: 29:20 (slow)
 
 ## AoC 2019
 
@@ -135,7 +137,8 @@ Solutions and utility script for Advent of Code challenges in Python.
 - Day 19: 40:00   (Way too slow! Oversight error. Come on.)
 - Day 20: days    (Not actually that hard but I struggled for no reason.) 
 - Day 21: days    (But it was super fun!)
-- Day 22:
+- Day 22: days    (Needed some help...)
+- Day 23:
 
 ## AoC 2020