diff --git a/2018/day12/day12.go b/2018/day12/day12.go
new file mode 100644
index 0000000..f0317c6
--- /dev/null
+++ b/2018/day12/day12.go
@@ -0,0 +1,185 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+var row map[int]bool
+var transitions []*Transition
+
+func main() {
+	inp := StdinToStringSlice()
+	BuildRow(inp[0])
+	for _, v := range inp[2:] {
+		transitions = append(transitions, NewTransition(v))
+	}
+	fmt.Print("St: ")
+	PrintState()
+	for i := 0; i < 20; i++ {
+		Tick()
+		fmt.Printf("%2d: ", i)
+		PrintState()
+	}
+	fmt.Println("Total:", GetSum())
+}
+
+func Tick() {
+	m := make(map[int]bool)
+	lowest, highest := 0, 0
+	for i := range row {
+		if i < lowest {
+			lowest = i
+		}
+		if i > highest {
+			highest = i
+		}
+	}
+	for i := lowest - 2; i <= highest+2; i++ {
+		m[i] = GetNextValue(i)
+	}
+	lowest, highest = 0, 0
+	for k := range m {
+		if k < lowest && m[k] {
+			lowest = k
+		}
+		if k > highest && m[k] {
+			highest = k
+		}
+	}
+	row = make(map[int]bool)
+	for i := lowest; i <= highest; i++ {
+		row[i] = m[i]
+	}
+}
+
+func GetSum() int {
+	var ret int
+	lowest, highest := 0, 0
+	for i := range row {
+		if i < lowest {
+			lowest = i
+		}
+		if i > highest {
+			highest = i
+		}
+	}
+	for i := lowest; i <= highest; i++ {
+		if row[i] {
+			ret += i
+		}
+	}
+	return ret
+}
+
+func BuildRow(inp string) {
+	inp = strings.Split(inp, ": ")[1]
+	row = make(map[int]bool)
+	for i, v := range inp {
+		row[i] = rb(v)
+	}
+}
+
+func GetIdxValue(idx int) byte {
+	var ret byte
+	for i := idx + 2; i >= idx-2; i-- {
+		ret = ret << 1
+		if row[i] {
+			ret = ret | 1
+		}
+	}
+	return ret
+}
+
+func GetNextValue(idx int) bool {
+	idxVal := GetIdxValue(idx)
+	for _, v := range transitions {
+		if v.GetValue() == idxVal {
+			return v.next
+		}
+	}
+	return false
+}
+
+func GetValueString(b byte) string {
+	var ret string
+	for i := 0; i < 5; i++ {
+		if (b & 1) == 1 {
+			ret = ret + "#"
+		} else {
+			ret = ret + "."
+		}
+		b = b >> 1
+	}
+	return ret
+}
+
+func PrintState() {
+	lowest, highest := -2, 30
+	for i := range row {
+		if i < lowest {
+			lowest = i
+		}
+		if i > highest {
+			highest = i
+		}
+	}
+	fmt.Print("(", lowest, ") ")
+	for i := lowest; i <= highest; i++ {
+		if row[i] {
+			fmt.Print("#")
+		} else {
+			fmt.Print(".")
+		}
+	}
+	fmt.Println(" (", highest, ") ")
+}
+
+type Transition struct {
+	state []bool
+	next  bool
+}
+
+func NewTransition(inp string) *Transition {
+	var state []bool
+	var next bool
+	pts := strings.Split(inp, " => ")
+	for i := len(pts[0]) - 1; i >= 0; i-- {
+		state = append(state, bb(pts[0][i]))
+	}
+	next = bb(pts[1][0])
+	t := &Transition{
+		state: state,
+		next:  next,
+	}
+	return t
+}
+
+func (t *Transition) GetValue() byte {
+	var ret byte
+	for _, v := range t.state {
+		ret = ret << 1
+		if v {
+			ret = ret | 1
+		}
+	}
+	return ret
+}
+
+func rb(r rune) bool {
+	return bb(byte(r))
+}
+func bb(b byte) bool {
+	return b == '#'
+}
+
+func StdinToStringSlice() []string {
+	var input []string
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		input = append(input, scanner.Text())
+	}
+	return input
+}
diff --git a/2018/day12/input b/2018/day12/input
new file mode 100644
index 0000000..1ae64d8
--- /dev/null
+++ b/2018/day12/input
@@ -0,0 +1,34 @@
+initial state: ##.#..########..##..#..##.....##..###.####.###.##.###...###.##..#.##...#.#.#...###..###.###.#.#
+
+####. => #
+##.#. => .
+.##.# => .
+..##. => .
+..... => .
+.#.#. => #
+.###. => .
+.#.## => .
+#.#.# => .
+.#... => #
+#..#. => #
+....# => .
+###.. => .
+##..# => #
+#..## => #
+..#.. => .
+##### => .
+.#### => #
+#.##. => #
+#.### => #
+...#. => .
+###.# => .
+#.#.. => #
+##... => #
+...## => #
+.#..# => .
+#.... => .
+#...# => .
+.##.. => #
+..### => .
+##.## => .
+..#.# => #
diff --git a/2018/day12/testinput b/2018/day12/testinput
new file mode 100644
index 0000000..864fa0c
--- /dev/null
+++ b/2018/day12/testinput
@@ -0,0 +1,16 @@
+initial state: #..#.#..##......###...###
+
+...## => #
+..#.. => #
+.#... => #
+.#.#. => #
+.#.## => #
+.##.. => #
+.#### => #
+#.#.# => #
+#.### => #
+##.#. => #
+##.## => #
+###.. => #
+###.# => #
+####. => #