better d17

day17/d17p2.swift

@@ -10,11 +10,6 @@ import Foundation
 6 bdv: A / 2^OP -> B
 7 cdv: A / 2^OP -> C
 
-adv 1 // A = A / 2
-out A // print(A % 8)
-jnz 0 // loop while A != 0
-
-
 2,4, 1,1, 7,5, 1,5, 4,0, 5,5, 0,3, 3,0
 bst 4 // B = A % 8
 bxl 1 // B = B xor 1
@@ -27,54 +22,16 @@ jnz 0 // loop while A != 0
 */
 
 extension RangeReplaceableCollection where Self: StringProtocol {
-    func paddingToLeft(upTo length: Int, using element: Element = " ") -> SubSequence {
-        return repeatElement(element, count: Swift.max(0, length-count)) + suffix(Swift.max(count, count-length))
-    }
-}
-
-let prog = [2,4, 1,1, 7,5, 1,5, 4,0, 5,5, 0,3, 3,0]
-
-var A0 = -1
-var Asuffixlen = 16
-var Asuffixes = [0b0110111010111101, 0b0110111110111101]
-var maxLen = 0
-aLoop: while true {
-    A0 += 1
-    for suffix in Asuffixes {
-        //var A = A0 // do this at the beginning to find the suffixes
-        let Ax = (A0 << Asuffixlen) | suffix
-        var A = Ax
-        var B = 0
-        var C = 0
-        progLoop: for i in 0..<prog.count {
-            B = A % 8  // 1
-            B = B ^ 1  // 2
-            C = A >> B // 3
-            B = B ^ 5  // 4
-            B = B ^ C  // 5
-            // print(B % 8, terminator: ",")
-            if B % 8 != prog[i] {
-                if i >= maxLen {
-                    maxLen = i
-                    print(String(Ax, radix: 2).paddingToLeft(upTo: 64) +
-                        " (\(i)) \(prog.prefix(i))")
-                }
-                continue aLoop
-            }
-            A = A >> 3
-            if A == 0 {
-                if i == prog.count - 1 {
-                    print(Ax)
-                    break aLoop
-                }
-                continue aLoop
-            }
-        }
+    func padLeft(to length: Int, using e: Element = " ") -> SubSequence {
+        return repeatElement(e,
+            count: Swift.max(0, length-count)) +
+                suffix(Swift.max(count, count-length)
+        )
     }
 }
 
 /*
-Loop 1
+printout 2
 B1 = A%8 | B2  | C3   | B4  | B5 = B4^C3 = xxxxx010 | A?
 ---------+-----+------+-----+-----------------------+------------
      000 | 001 | A>>1 | 100 | 100^(A>>1) = xxxxx010 | ...xxxx001x (❌)
@@ -85,16 +42,67 @@ B1 = A%8 | B2  | C3   | B4  | B5 = B4^C3 = xxxxx010 | A?
      101 | 100 | A>>4 | 001 | 001^(A>>4) = xxxxx010 | ...x011x101
      110 | 111 | A>>7 | 010 | 010^(A>>7) = xxxxx010 | .000xxxx110
      111 | 110 | A>>6 | 011 | 011^(A>>6) = xxxxx010 | ..001xxx111
-
-Loop 2
-B1 = A%8 | B2  | C3   | B4  | B5 = B4^C3 = xxxxx100 | A?
----------+-----+------+-----+-----------------------+---------
-     000 | 001 | A>>1 | 100 | 100^(A>>1) = xxxxx100 | ...xxxx0000
-     001 | 000 | A    | 101 | 101^A      = xxxxx100 | ...xxxxx001
-     010 | 011 | A>>3 | 110 | 110^(A>>3) = xxxxx100 | ...xx010010
-     011 | 010 | A>>2 | 111 | 111^(A>>2) = xxxxx100 | ...xxx011xx (❌)
-     100 | 101 | A>>5 | 000 | 000^(A>>5) = xxxxx100 | 010xx100
-     101 | 100 | A>>4 | 001 | 001^(A>>4) = xxxxx100 | 0011x101
-     110 | 111 | A>>7 | 010 | 010^(A>>7) = xxxxx100 | 0xxxx110
-     111 | 110 | A>>6 | 011 | 011^(A>>6) = xxxxx100 | 01xxx111
 */
+
+struct Register : Comparable, CustomStringConvertible {
+    let value: Int
+    let mask: Int
+    var description: String {
+        var s: String = ""
+        var (v, m) = (value, mask)
+        while v != 0 || m != 0 {
+            s = ((m&1 == 0) ? "x" : String(v&1)) + s
+            v >>= 1
+            m >>= 1
+        }
+        return String(s.padLeft(to: 64, using: "x"))
+    }
+    static func < (lhs: Register, rhs: Register) -> Bool {
+        return (lhs.value & lhs.mask) < (rhs.value & rhs.mask)
+    }
+    static func == (lhs: Register, rhs: Register) -> Bool {
+        return (lhs.value & lhs.mask) == (rhs.value & rhs.mask)
+    }
+    var dec: Int { return value & mask }
+
+    func combine(with b: Register) -> Register? {
+        if self.value & self.mask & b.mask == b.value & self.mask & b.mask {
+            return Register(
+                value: (self.value & self.mask) | (b.value & b.mask),
+                mask: self.mask | b.mask
+            )
+        }
+        return nil
+    }
+    static func >> (lhs: Register, rhs: Int) -> Register {
+        return Register(value: lhs.value >> rhs, mask: lhs.mask >> rhs)
+    }
+    static func << (lhs: Register, rhs: Int) -> Register {
+        return Register(value: lhs.value << rhs, mask: lhs.mask << rhs)
+    }
+}
+
+func possibleAs(fromB5 b5Suffix: Int) -> [Register] {
+    let choices: [Register] = (0b000...0b111).compactMap { aSuffix in
+        let aShift = aSuffix ^ 1
+        let b4 = aShift ^ 5
+        let a = Register(value: (b4^b5Suffix) << aShift, mask: 0b111 << aShift)
+        return a.combine(with: Register(value: aSuffix, mask: 0b111))
+    }
+    return choices.sorted()
+}
+
+func findA(from a: Register, _ outputs: [Int]) -> [Register] {
+    if outputs.count == 0 { return [a] }
+    let As = possibleAs(fromB5: outputs[0]).compactMap { a.combine(with: $0) }
+    return As.flatMap { a in 
+        findA(from: a >> 3, Array(outputs.dropFirst())).compactMap { nextA in
+            a.combine(with: nextA << 3)
+        }
+    }.sorted()
+}
+
+let prog = [2,4, 1,1, 7,5, 1,5, 4,0, 5,5, 0,3, 3,0]
+let res = findA(from: Register(value: 0, mask: 0), prog)
+print(res)
+print(res[0].dec)