diff --git a/16/16.go b/16/16.go
new file mode 100644
index 0000000..f5c9478
--- /dev/null
+++ b/16/16.go
@@ -0,0 +1,141 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type instruction struct {
+	instr    byte
+	arg1    int
+	arg2    int
+	n1	byte
+	n2	byte
+}
+
+// cat input | go run 16.go
+
+func main() {
+
+	scanner := bufio.NewScanner(os.Stdin)
+
+	for scanner.Scan() {
+		instr := ParseInstr(strings.Split(scanner.Text(), ","))
+
+		input := "abcdefghijklmnop"
+		seen := make(map[string]string)
+
+		fmt.Println(string(Run16(input, instr)))
+		rounds := 1000000000
+
+		for i := 1; i <= rounds; i++ {
+			if i % (rounds/10) == 0 {
+				fmt.Print("/")
+			} else if i % (rounds/100) == 0 {
+				fmt.Print(".")
+			}
+			
+			// Cache known results. Suspect we could cache repeating patterns, but this is fast enough.
+			cache, exists := seen[input]
+			if exists {
+				input = cache
+			} else {
+				pre := input
+				input = Run16(input,instr)
+				seen[pre] = input
+			}
+		}
+
+		fmt.Println()
+		fmt.Println(input)
+	}
+}
+
+func Run16(i string, instr []instruction) string {
+	input := []byte(i)
+	//fmt.Println(i)
+	for i := range instr {
+		if instr[i].instr == 's' {
+			input = Spin(input, instr[i].arg1)
+		}
+		if instr[i].instr == 'x' {
+			input = SwapPos(input, instr[i].arg1, instr[i].arg2)
+		}
+		if instr[i].instr == 'p' {
+			input = SwapName(input, instr[i].n1, instr[i].n2)
+		}
+	}
+	return string(input)
+}
+
+func Spin(input []byte, pos int) []byte {
+	//fmt.Println("Spin", input, pos)
+	t := make([]byte, len(input))
+
+	p := 0
+	for i := len(input)-pos; i < len(input); i++ {
+		t[p] = input[i]
+		p++
+	}
+	for i := 0; i < len(input)-pos; i++ {
+		t[p] = input[i]
+		p++
+	}
+
+	return t
+}
+
+func SwapPos(ia []byte, a int, b int) []byte {
+	//fmt.Println("SwapPos", input, args)
+	ia[a],ia[b] = ia[b],ia[a]
+	return ia
+}
+
+func SwapName(ia []byte, s1 byte, s2 byte) []byte {
+	//fmt.Println("SwapName", ia, s1, s2)
+	a:= -1
+	b:= -1
+
+	for i := 0; i < len(ia); i++ {
+		if ia[i] == s1 {
+			a = i
+		}
+		if ia[i] == s2 {
+			b = i
+		}
+		if a != -1 && b != -1 {
+			break
+		}
+	}
+
+	ia[a],ia[b] = ia[b],ia[a]
+	return ia
+}
+
+func ParseInstr(l []string) []instruction {
+	var instructions []instruction
+	for i := range l {
+		var res = instruction{0, 0, 0, 0, 0}
+
+		res.instr = l[i][0]
+
+		if l[i][0] == 's' {
+			res.arg1,_ = strconv.Atoi( l[i][1:len(l[i])] )
+		}
+		if l[i][0] == 'x' {
+			s := strings.Split(l[i][1:len(l[i])], "/")
+			res.arg1,_ = strconv.Atoi(s[0])
+			res.arg2,_ = strconv.Atoi(s[1])
+		}
+		if l[i][0] == 'p' {
+			s := strings.Split(l[i][1:len(l[i])], "/")
+			res.n1 = s[0][0]
+			res.n2 = s[1][0]
+		}
+		instructions = append(instructions, res)
+	}
+	return instructions
+}
\ No newline at end of file
diff --git a/16/16_test.go b/16/16_test.go
new file mode 100644
index 0000000..52f860b
--- /dev/null
+++ b/16/16_test.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"testing"
+)
+
+var test = []string{"s1", "x3/4", "pe/b"}
+
+func TestRun16(t *testing.T) {
+	i := ParseInstr(test)
+	input := "abcde"
+	v := Run16(input, i)
+	if v != "baedc" {
+		t.Error(
+			"For", test,
+			"expected baedc",
+			"got", v,
+		)
+	}
+}
+
+func TestRun1M(t *testing.T) {
+	i := ParseInstr(test)
+	input := "abcdefghijlmnop"
+
+	for x :=0; x<10000000; x++ {
+		input = Run16(input, i)
+	}
+
+	if input != "fghdijlmnopabce" {
+		t.Error(
+			"For", test,
+			"expected fghdijlmnopabce",
+			"got", input,
+		)
+	}
+}
\ No newline at end of file