Add solution to 2024-12-17

Author: fuglede

2024/day17/solutions.py

@@ -0,0 +1,73 @@
+from itertools import count
+
+program = [2, 4, 1, 1, 7, 5, 1, 5, 4, 5, 0, 3, 5, 5, 3, 0]
+
+
+def run(A):
+    ptr = 0
+    B = 0
+    C = 0
+    result = []
+    while True:
+        try:
+            ins = program[ptr]
+            op = program[ptr + 1]
+        except:
+            return result
+        if op <= 3:
+            combo = op
+        elif op == 4:
+            combo = A
+        elif op == 5:
+            combo = B
+        elif op == 6:
+            combo = C
+
+        match ins:
+            case 0:
+                A //= 2**combo
+            case 1:
+                B ^= op
+            case 2:
+                B = combo % 8
+            case 3:
+                if A != 0:
+                    ptr = op - 2
+            case 4:
+                B ^= C
+            case 5:
+                result.append(combo % 8)
+            case 6:
+                B = A // (2**combo)
+            case 7:
+                C = A // (2**combo)
+        ptr += 2
+
+
+# Part 1
+print(run(30344604))
+
+
+# Part 2
+mid = int(next(A for i in count() if len(run(A := 10**i)) == len(program))) * 10
+width = mid
+spacing = width // 1000
+for matching_digits in range(1, len(program) + 1):
+    for A in range(mid - width, mid + width, spacing):
+        res = run(A)
+        if (
+            len(res) == len(program)
+            and res[-matching_digits:] == program[-matching_digits:]
+        ):
+            break
+    else:
+        assert False
+    mid = A
+    spacing //= 10
+    width //= 10
+    if spacing <= 10:
+        spacing = 1
+    if width <= 10000:
+        width = 100000
+
+print(A)