diff --git a/day17/copy.go b/day17/copy.go
deleted file mode 100644
index f55d6fd..0000000
--- a/day17/copy.go
+++ /dev/null
@@ -1,157 +0,0 @@
-package main
-
-import ("math"; "errors"; "strconv"; "strings"; "fmt"; "os")
-
-//---------------------------------------------------------
-func check(err error) { if err != nil { panic(err) } }
-
-//---------------------------------------------------------
-type Computer struct {
-    pc   uint
-    ra   uint
-    rb   uint
-    rc   uint
-    mem []byte
-}
-
-func NewComputer(input string) *Computer {
-    registers := strings.Split(input, "\n\n")[0]
-    memory    := strings.Split(strings.Split(input, "\n\n")[1], " ")[1]
-
-    lines := strings.Split(registers, "\n")
-    ra, err := strconv.Atoi(strings.TrimSpace(strings.Split(lines[0], ":")[1]))
-    check(err)
-    rb, err := strconv.Atoi(strings.TrimSpace(strings.Split(lines[1], ":")[1]))
-    check(err)
-    rc, err := strconv.Atoi(strings.TrimSpace(strings.Split(lines[2], ":")[1]))
-    check(err)
-
-    mem := make([]byte, 0)
-    for _, str := range strings.Split(memory, ",") {
-        num, err := strconv.Atoi(str)
-        check(err)
-        mem = append(mem, byte(num))
-    }
-
-    return &Computer{
-        pc: 0,
-        ra: uint(ra),
-        rb: uint(rb),
-        rc: uint(rc),
-        mem: mem,
-    }
-}
-
-func (c *Computer) literalop() uint {
-    // current literal operator
-    return uint(c.mem[c.pc + 1])
-}
-
-func (c *Computer) comboop() uint {
-    // current combo operator
-    val := uint(c.mem[c.pc + 1])
-
-    switch {
-        case val == 4: val = c.ra
-        case val == 5: val = c.rb
-        case val == 6: val = c.rc
-        case val == 7: panic("invalid program")
-    }
-
-    return val
-}
-
-func (c *Computer) adv(op uint) uint {
-    // division
-    numerator   := c.ra
-    denominator := math.Pow(2, float64(op))
-    return uint(float64(numerator) / float64(denominator))
-}
-
-func (c *Computer) bxl(op uint) uint {
-    // bitwise xor
-    return c.rb ^ op
-}
-
-func (c *Computer) bst(op uint) uint {
-    // mod 8
-    return op % 8
-}
-
-func (c *Computer) jnz(op uint) {
-    // jump if non zero
-    if c.ra == 0 {  
-        return
-    } else {
-        c.pc = op - 2
-        return
-    }
-}
-
-func (c *Computer) bxc() uint {
-    // bitwise xor
-    return c.rb ^ c.rc
-}
-
-func (c *Computer) tick() (int, error) {
-    // returns an error if the program halts
-    if c.pc >= uint(len(c.mem)) { return -1, errors.New("halted") }
-
-    instr := c.mem[c.pc]
-    out := -1
-    switch {
-        case instr == 0: c.ra = c.adv(c.comboop())
-        case instr == 1: c.rb = c.bxl(c.literalop())
-        case instr == 2: c.rb = c.bst(c.comboop())
-        case instr == 3: c.jnz(c.literalop())
-        case instr == 4: c.rb = c.bxc()
-        case instr == 5: out = int(c.comboop() % 8)
-        case instr == 6: c.rb = c.adv(c.comboop())
-        case instr == 7: c.rc = c.adv(c.comboop())
-    }
-
-    c.pc += 2
-    return out, nil
-}
-
-func (c *Computer) returns_its_source() bool {
-    i := 0
-    for {
-        out, err := c.tick()
-
-        if err != nil { return false }
-        if out != -1 {
-            if byte(out) != c.mem[i] { return false }
-            i++
-            if i == len(c.mem) { return true  }
-        } 
-    }
-    // never reached
-    return false
-}
-
-func (c *Computer) restore(ra uint) {
-    c.pc = 0
-    c.ra = ra
-    c.rb = 0
-    c.rc = 0
-}
-
-
-//---------------------------------------------------------
-func main() {
-    dat, err := os.ReadFile("data.txt")
-    check(err)
-    input := strings.TrimSpace(string(dat))
-
-    comp := NewComputer(input)
-
-    for i := range 1000000000 {
-        comp.restore(uint(i))
-        if comp.returns_its_source() {
-            fmt.Println(i)
-            break
-        }
-    }
-}
-
diff --git a/day17/reversed.go b/day17/reversed.go
new file mode 100644
index 0000000..a694104
--- /dev/null
+++ b/day17/reversed.go
@@ -0,0 +1,107 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func reverseSlice(slice []uint) {
+	for i, j := 0, len(slice)-1; i < j; i, j = i+1, j-1 {
+		slice[i], slice[j] = slice[j], slice[i]
+	}
+}
+
+func compressedProgram(ra uint) []uint {
+	out := make([]uint, 0)
+
+	var A, B uint
+	A = ra
+
+	for {
+		B = ((A % 8) ^ 2) ^ 7 ^ (A >> ((A % 8) ^ 2))
+		A = A >> 3
+
+		out = append(out, B%8)
+
+		if A == 0 {
+			break
+		}
+	}
+
+	return out
+}
+
+func reversedProgram(out []uint) uint {
+	reverseSlice(out)
+	A := uint(0)
+
+	for _, o := range out {
+    
+		// find next n bits so that o is returned
+        n := 2
+        searching := true
+        for searching {
+            n++
+
+            // for every combination of n bits
+		    for i := range 1 << n {
+                A_ := (A << n) + uint(i)
+
+                //fmt.Println("add", i, "as binary with", n, "bits")
+		    	//fmt.Println("old", strconv.FormatUint(uint64(A), 2))
+		    	//fmt.Println("new", strconv.FormatUint(uint64(A_), 2))
+
+		    	if o == ((A_%8)^2)^7^(A_>>((A_%8)^2))%8 {
+		    		A = A_
+		    	    //fmt.Println("valid")
+		    		//fmt.Println("yields", compressedProgram(A))
+                    searching = false
+		    		break
+		    	}
+
+		    	//fmt.Println("invalid")
+		    }
+        }
+
+	}
+	return A
+}
+
+func main() {
+	/*
+
+
+		fmt.Println(input)
+
+		a := uint64(0)
+		for _, elem := range input {
+
+			expected_d := elem ^ 7
+			for b := range 8 {
+				e := uint64(b ^ 2)
+				c := (((a << 3) | uint64(b)) >> (e)) % 8
+				actual_d := c ^ e
+				if uint64(expected_d) == actual_d {
+					fmt.Println(b)
+					fmt.Println(e)
+					fmt.Println(c)
+					a = a << 3
+					a = a | uint64(b)
+					fmt.Println(strconv.FormatUint(a, 2))
+					fmt.Println(a, 2)
+					break
+				}
+			}
+
+		}
+		fmt.Println(a)
+		//fmt.Println(strconv.FormatUint(a, 2))
+	*/
+
+	//fmt.Println(compressedProgram(41644071))
+
+	input := []uint{2, 4, 1, 2, 7, 5, 1, 7, 4, 4, 0, 3, 5, 5, 3, 0}
+	fmt.Println("-- input: ", input, "--")
+	ra := reversedProgram(input)
+	fmt.Println("-- ra:    ", ra, "--")
+}