use the the actual Run method for part2 making it input agnostic

Author: encse

2024/Day17/README.md

@@ -21,6 +21,7 @@ There is _some interconnection_ between the consecutive numbers, so one cannot j
 for each. But I was able to come up with a _recursive solution_ that generates the input _backwards_. Once we know the 
 higher bits, we can try all combinations for the next 3 bits, and so on down to the first bit.
 
-As an added bonus I implemented (part of) the emulator in [VIC-20 BASIC](https://hu.wikipedia.org/wiki/Commodore_VIC-20). This is how it runs the second sample that prints out its own source code.
+As an added bonus I implemented (part of) the emulator in [VIC-20 BASIC](https://hu.wikipedia.org/wiki/Commodore_VIC-20). 
+This is how it runs the second sample that prints out its own source code.
 
 ![vic20.gif](vic20.gif)

2024/Day17/Solution.cs

@@ -11,61 +11,60 @@ enum Opcode {
         Adv, Bxl, Bst, Jnz, Bxc, Out, Bdv, Cdv
     }
 
-    public object PartOne(string input) => Run(input);
-    public object PartTwo(string input) => GenerateA(Parse(input).program.ToList()).Min();
-
-    string Run(string input) {
+    public object PartOne(string input) {
         var (state, program) = Parse(input);
-        var combo = (long op) => op < 4 ? (int)op : (int)state[op - 4];
-        var res = new List<int>();
-        for (var ip = 0; ip < program.Length; ip += 2) {
-            switch ((Opcode)program[ip], program[ip + 1]) {
-                case (Opcode.Adv, var op): state[0] = state[0] >> combo(op); break;
-                case (Opcode.Bdv, var op): state[1] = state[0] >> combo(op); break;
-                case (Opcode.Cdv, var op): state[2] = state[0] >> combo(op); break;
+        return string.Join(",", Run(state, program));
+    } 
+    public object PartTwo(string input) {
+        var (_, program) = Parse(input);
+        return GenerateA(program, program).Min();
+    }
+
+    List<long> Run(List<long> state, List<long> program) {
+        var combo = (int op) => op < 4 ? op : state[op - 4];
+        var res = new List<long>();
+        for (var ip = 0; ip < program.Count; ip += 2) {
+            switch ((Opcode)program[ip], (int)program[ip + 1]) {
+                case (Opcode.Adv, var op): state[0] = state[0] >> (int)combo(op); break;
+                case (Opcode.Bdv, var op): state[1] = state[0] >> (int)combo(op); break;
+                case (Opcode.Cdv, var op): state[2] = state[0] >> (int)combo(op); break;
                 case (Opcode.Bxl, var op): state[1] = state[1] ^ op; break;
                 case (Opcode.Bst, var op): state[1] = combo(op) % 8; break;
-                case (Opcode.Jnz, var op): ip = state[0] == 0 ? ip : (int)op - 2; break;
+                case (Opcode.Jnz, var op): ip = state[0] == 0 ? ip : op - 2; break;
                 case (Opcode.Bxc, var op): state[1] = state[1] ^ state[2]; break;
                 case (Opcode.Out, var op): res.Add(combo(op) % 8); break;
             }
         }
-        return string.Join(",", res);
+        return res;
     }
 
     /*
-        Determines register A for the given output. The search works recursively and in reverse order, 
-        starting from the last number to be printed and ending with the first.
+        Determines register A for the given output. The search works recursively and in 
+        reverse order, starting from the last number to be printed and ending with the first.
     */
-    IEnumerable<long> GenerateA(List<long> output) {
+    IEnumerable<long> GenerateA(List<long> program, List<long> output) {
         if (!output.Any()) {
             yield return 0;
             yield break;
         }
 
-        // this loop is pretty much the assembly code of the program reimplemented in c#
-        foreach (var ah in GenerateA(output[1..])) {
+        foreach (var ah in GenerateA(program, output[1..])) {
             for (var al = 0; al < 8; al++) {
                 var a = ah * 8 + al;
-                long b = a % 8;
-                b = b ^ 3;
-                var c = a >> (int)b;
-                b = b ^ c;
-                b = b ^ 5;
-                if (output[0] == b % 8) {
+                if (Run([a, 0, 0], program).SequenceEqual(output)) {
                     yield return a;
                 }
             }
         }
     }
 
-    (long[] state, long[] program) Parse(string input) {
+    (List<long> state, List<long> program) Parse(string input) {
         var blocks = input.Split("\n\n").Select(ParseNums).ToArray();
         return (blocks[0], blocks[1]);
     }
 
-    long[] ParseNums(string st) =>
+    List<long> ParseNums(string st) =>
         Regex.Matches(st, @"\d+", RegexOptions.Multiline)
             .Select(m => long.Parse(m.Value))
-            .ToArray();
+            .ToList();
 }