1 files changed, 56 insertions, 67 deletions
diff --git a/2024/17/python/main.py b/2024/17/python/main.py
index 7e8ecb1..a441d40 100644
--- a/2024/17/python/main.py
+++ b/2024/17/python/main.py
@@ -1,77 +1,66 @@
 from fileinput import input
-from itertools import takewhile
+from itertools import takewhile, zip_longest
 
 inp = map(str.strip, input())
-regs = {r[1][0]: int(r[2]) for r in (line.split() for line in takewhile(bool, inp))}
+regs = [int(r[2]) for r in (line.split() for line in takewhile(bool, inp))]
 prog = [int(o) for o in next(inp).split()[1].split(",")]
 out = []
 
-ir = 0
-combo = {
-    0: lambda: 0,
-    1: lambda: 1,
-    2: lambda: 2,
-    3: lambda: 3,
-    4: lambda: regs["A"],
-    5: lambda: regs["B"],
-    6: lambda: regs["C"],
-    7: None,
-}
 
-
-def _adv(op):
-    regs["A"] = regs["A"] >> combo[op]()
-
-
-def _bxl(op):
-    regs["B"] ^= op
-
-
-def _bst(op):
-    regs["B"] = combo[op]() & 0b111
-
-
-def _jnz(op):
-    global ir
-    if regs["A"]:
-        ir = op
-        ir -= 2  # Undo IR
-
-
-def _bxc(_):
-    regs["B"] ^= regs["C"]
-
-
-def _out(op):
-    out.append(combo[op]() & 0b111)
-
-
-def _bdv(op):
-    regs["B"] = regs["A"] >> combo[op]()
-
-
-def _cdv(op):
-    regs["C"] = regs["A"] >> combo[op]()
-
-
-instrs = {
-    0: _adv,
-    1: _bxl,
-    2: _bst,
-    3: _jnz,
-    4: _bxc,
-    5: _out,
-    6: _bdv,
-    7: _cdv,
-}
-
-while ir <= len(prog) - 1:
-    inst, op = prog[ir], prog[ir + 1]
-    instrs[inst](op)
-    ir += 2
-
-silver = ",".join(map(str, out))
-gold = 0
+def run(prog, ra, rb, rc):
+    out = []
+    ir = 0
+    while ir < len(prog):
+        instr, op = prog[ir], prog[ir + 1]
+        combo = {4: ra, 5: rb, 6: rc}
+        cop = combo.get(op, op)
+        match instr:
+            case 0:
+                ra = ra >> cop
+            case 1:
+                rb ^= op
+            case 2:
+                rb = cop & 0b111
+            case 3 if ra:
+                ir = op - 2
+            case 4:
+                rb ^= rc
+            case 5:
+                yield cop & 0b111
+            case 6:
+                rb = ra >> cop
+            case 7:
+                rc = ra >> cop
+        ir += 2
+    return out
+
+
+def match(prog, ra):
+    return (
+        got == want
+        for got, want in zip_longest(
+            reversed(list(run(prog, ra, 0, 0))),
+            reversed(prog),
+        )
+    )
+
+
+def find_a(prog):
+    q = list(range(8))
+    while True:
+        curr = q.pop(0)
+        if all(match(prog, curr)):
+            return curr
+
+        best = sum(match(prog, curr))
+        for n in range(8):
+            ra = (curr << 3) + n
+            if sum(match(prog, ra)) > best:
+                q.append(ra)
+
+
+silver = ",".join(map(str, run(prog, *regs)))
+gold = find_a(prog)
 
 print("silver:", silver)
 print("gold:", gold)