Finish 2015.

2015/d19.py

@@ -1,41 +1,41 @@
-import sys
-from random import shuffle
-
-data = open(0).read().strip()
+with open("i19.txt", "r") as f:
+    data = f.read()
 
 eqs = []
-text = ""
+molecule = ""
 for line in data.splitlines():
     if "=>" in line:
         lhs, rhs = line.split(" => ")
         eqs.append((lhs, rhs))
     elif line:
-        text = line
+        molecule = line.strip()
 
 molecules = set()
 for lhs, rhs in eqs:
-    for i in range(len(text)):
-        f, t = text[:i], text[i:]
+    for i in range(len(molecule)):
+        f, t = molecule[:i], molecule[i:]
         if t.startswith(lhs):
             n = f + t.replace(lhs, rhs, 1)
             molecules.add(n)
 print(len(molecules))
 
-# m = float("inf")
-# for _ in range(100000):
-#     getout = False
-#     c = str(text)
-#     for i in range(10**4):
-#         if i % 1000 == 0:
-#             shuffle(eqs)
-#         for lhs, rhs in eqs:
-#             if rhs in c:
-#                 c = c.replace(rhs, lhs, 1)
-#                 if c == "e":
-#                     if i < m:
-#                         m = i
-#                         print(i)
-#                     getout = True
-#         if getout:
-#             break
-# print(m)
+
+# It seems like the problem input is specifically designed so that reversing
+# the molecule back to 'e' works by simply replacing RHS with LHS continuously.
+# Intuitively, it seems like this should not work in many cases or at least not
+# result in the shortest sequence. Probably I am just salty that it took me so
+# long to find this trivial solution.
+x = molecule
+count = 0
+while len(x) > 1:
+    old_len = len(x)
+    for lhs, rhs in eqs:
+        if rhs in x:
+            x = x.replace(rhs, lhs, 1)
+            count += 1
+            break
+    else:
+        break
+
+assert x == 'e'
+print(count)

2015/d23.py

@@ -0,0 +1,40 @@
+
+insts = []
+with open("i23.txt", "r") as f:
+    for line in f:
+        args = line.strip().replace(",", "").split()
+        insts.append(args)
+
+part_2 = True
+i = 0
+regs = {"a": 0, "b": 0}
+if part_2:
+    regs["a"] = 1
+
+while i < len(insts):
+    inst = insts[i]
+    match inst:
+        case ["inc", reg]:
+            regs[reg] += 1
+        case ["hlf", reg]:
+            regs[reg] //= 2
+        case ["tpl", reg]:
+            regs[reg] *= 3
+        case ["jio", reg, offset]:
+            if regs[reg] == 1:
+                i += int(offset)
+                continue
+        case ["jie", reg, offset]:
+            offset = int(offset)
+            if regs[reg] % 2 == 0:
+                i += int(offset)
+                continue
+        case ["jmp", offset]:
+            i += int(offset)
+            continue
+        case _:
+            print(inst)
+            assert False
+    i += 1
+
+print(regs["b"])

2015/d24.py

@@ -0,0 +1,46 @@
+import sys
+from itertools import combinations
+
+with open("i24.txt", "r") as f:
+    weights = list(map(int, f.readlines()))
+
+total_sum = sum(weights)
+
+indices = list(range(len(weights)))
+
+lowest = None
+def find(part_1=True):
+    if part_1:
+        target_weight = total_sum // 3
+    else:
+        target_weight = total_sum // 4
+    for group_1_size in range(1, len(weights) - 1):
+        for group_1_indices in combinations(indices, group_1_size):
+            group_1_weight = sum(weights[i] for i in group_1_indices)
+            if not group_1_weight == target_weight:
+                continue
+            remaining_indices = list(set(indices) - set(group_1_indices))
+            for group_2_size in range(1, len(remaining_indices) - 1):
+                for group_2_indices in combinations(remaining_indices, group_2_size):
+                    group_2_weight = sum(weights[i] for i in group_2_indices)
+                    if not group_2_weight == target_weight:
+                        continue
+                    if part_1 :
+                        r = 1
+                        for i in group_1_indices:
+                            r *= weights[i]
+                        return r
+                    else:
+                        remaining_indices = list(set(indices) - set(group_1_indices))
+                        for group_3_size in range(1, len(remaining_indices)- 1):
+                            for group_3_indices in combinations(remaining_indices, group_3_size):
+                                group_3_weight = sum(weights[i] for i in group_3_indices)
+                                if not group_3_weight == target_weight:
+                                    continue
+                                r = 1
+                                for i in group_1_indices:
+                                    r *= weights[i]
+                                return r
+
+print(find(True))
+print(find(False))

2015/d25.py

@@ -0,0 +1,19 @@
+import sys
+from lib import str_to_ints
+
+with open("i25.txt", "r") as f:
+    target_row, target_col = str_to_ints(f.read())
+
+x = 20151125
+m = 252533
+d = 33554393
+
+for start_row in range(1, 10000):
+    row, col = start_row, 1
+    while row > 0:
+        if row == target_row and col == target_col:
+            print(x)
+            sys.exit(0)
+        x = (x * m) % d
+        row -= 1
+        col += 1