diff --git a/2021/day18/input b/2021/day18/input
new file mode 100644
index 0000000..7b3edd7
--- /dev/null
+++ b/2021/day18/input
@@ -0,0 +1,100 @@
+[[[0,[6,6]],[[7,2],[6,2]]],[[[9,4],[5,8]],6]]
+[[[4,9],6],[[[0,1],[8,5]],[3,[7,6]]]]
+[[1,7],[[[1,3],2],[[6,8],8]]]
+[4,[[6,[6,0]],[[4,9],5]]]
+[[3,8],[[0,6],1]]
+[[2,2],[[[2,3],[2,9]],[[9,6],[4,9]]]]
+[[[3,4],[[7,7],[7,8]]],[[0,2],6]]
+[[[[4,4],[3,3]],[[9,0],4]],[8,[7,[6,6]]]]
+[[[9,9],8],1]
+[2,[[7,[1,9]],[9,2]]]
+[[[[6,0],[8,2]],[[9,0],[8,7]]],[3,[6,[8,8]]]]
+[[[8,[9,2]],[1,4]],[[2,2],[[1,0],5]]]
+[[[9,[0,3]],[4,[2,3]]],[[8,[0,1]],[[4,8],[5,4]]]]
+[[[2,0],[1,7]],[[3,[0,7]],[[7,6],0]]]
+[[[1,[5,1]],[[0,3],9]],[[3,8],[[5,3],1]]]
+[[[[4,5],2],[[7,7],[4,8]]],[3,[3,[6,5]]]]
+[[[[4,4],4],[[5,0],2]],[9,[[0,7],5]]]
+[[2,[[8,0],9]],0]
+[[[[0,5],[1,0]],[0,[5,1]]],[[[0,8],[6,0]],[6,[3,9]]]]
+[[[[2,4],[5,5]],[4,7]],[[[5,6],[9,5]],1]]
+[[[4,[5,1]],[[6,7],1]],[1,[[5,9],4]]]
+[[0,6],[[9,3],[4,2]]]
+[7,[[[2,4],[3,4]],[2,0]]]
+[0,[6,7]]
+[[[0,2],[[7,2],7]],[[[6,3],[2,0]],[[8,6],[7,9]]]]
+[[[7,[0,5]],7],[[2,3],[3,3]]]
+[[2,[0,[4,5]]],[[4,[7,9]],[[5,6],4]]]
+[[[5,4],0],[5,[[7,1],[7,6]]]]
+[[0,3],[[[5,2],5],[[8,5],[2,8]]]]
+[[[0,[8,9]],[[3,1],2]],[[3,[7,1]],7]]
+[[[[9,7],[5,5]],[[2,4],1]],[[1,3],[[4,0],[9,1]]]]
+[[[0,9],4],0]
+[[[[8,8],9],[[8,2],3]],[[2,[7,4]],[9,1]]]
+[[[1,2],8],[[[4,4],2],[2,4]]]
+[[6,[7,[2,1]]],[[2,1],3]]
+[0,[[[7,8],0],[5,[8,5]]]]
+[[[2,8],6],[6,[[1,1],[1,2]]]]
+[[[[3,9],2],[7,[4,9]]],[[[5,3],3],[[7,3],5]]]
+[[2,[4,[3,2]]],[[4,9],6]]
+[[[[1,1],[0,5]],[1,[4,9]]],[[6,[5,7]],[[1,6],[7,2]]]]
+[0,[0,[[8,5],8]]]
+[[[1,[2,5]],8],[[3,[0,2]],4]]
+[[[4,3],0],[[[6,9],[7,2]],[[1,9],8]]]
+[[[[7,1],0],[7,5]],[6,2]]
+[[[9,[6,5]],6],[[5,5],[[4,6],2]]]
+[[[[3,0],[5,5]],2],[7,[9,[8,5]]]]
+[9,[[9,7],[3,3]]]
+[[[0,0],4],[7,[[5,8],[2,7]]]]
+[[[[9,2],4],[[0,1],[4,1]]],[[4,[6,5]],5]]
+[8,[[[5,2],8],[6,0]]]
+[[[[9,6],2],9],[5,[[5,3],5]]]
+[[[8,[8,0]],[7,[3,3]]],[[[8,8],[5,5]],[[1,3],3]]]
+[[[2,3],4],[[[8,8],[1,4]],5]]
+[[[[3,7],9],6],[[5,[4,1]],4]]
+[[[3,4],[[5,3],4]],[[2,[4,2]],[[0,7],5]]]
+[0,9]
+[[2,[[9,1],[3,4]]],[[[5,7],[6,6]],[5,[3,6]]]]
+[[[[7,2],7],[[8,7],9]],[9,[[7,0],[3,4]]]]
+[[[[8,3],[0,2]],0],[5,[[9,9],1]]]
+[[[1,5],[[3,9],[5,6]]],[6,[2,[2,4]]]]
+[[[[1,6],7],[8,9]],[[[6,7],8],1]]
+[[5,[[1,3],[1,8]]],[8,1]]
+[[[[4,6],9],[[3,0],[2,4]]],3]
+[[[[6,6],[9,8]],[4,7]],[[6,8],1]]
+[[[9,[7,8]],[4,[0,3]]],[[8,[8,1]],8]]
+[4,0]
+[[[[1,8],[6,9]],[[1,5],[6,1]]],[[1,9],[0,1]]]
+[[[[1,8],[1,8]],[[6,2],[8,6]]],[[[6,8],3],[[8,0],[7,3]]]]
+[8,9]
+[[2,8],2]
+[[4,[[7,0],[1,8]]],1]
+[[5,0],[[[3,4],0],3]]
+[[[[7,5],2],6],[[9,2],[[5,0],[7,5]]]]
+[[8,[[0,0],[3,7]]],[1,6]]
+[[[[5,2],[5,1]],[8,6]],[2,[9,[5,4]]]]
+[[[6,[3,3]],[[0,4],0]],[[4,4],[[3,6],6]]]
+[[7,[[4,9],[9,7]]],[3,[[8,7],9]]]
+[[[[3,3],9],[8,[7,2]]],[[3,9],8]]
+[[[0,[9,2]],1],[6,[[9,7],8]]]
+[[5,[0,1]],[8,7]]
+[[[[0,7],5],8],[[[0,0],[7,1]],[2,[6,9]]]]
+[[5,[[3,3],7]],[[[1,3],[5,4]],[[0,8],[2,2]]]]
+[[[[7,4],5],[[9,1],[5,5]]],[[0,8],[0,[6,4]]]]
+[[0,[[9,5],[4,3]]],[[[2,7],[4,7]],6]]
+[[7,[[3,2],[7,9]]],[[[8,6],[1,8]],[5,[5,6]]]]
+[[0,[[3,3],0]],[[[5,2],[2,4]],[6,8]]]
+[[[6,[5,6]],9],[[[5,2],7],[[8,7],[2,4]]]]
+[[[[7,2],[8,2]],5],[[[4,5],[0,7]],6]]
+[[[[6,1],4],6],[[4,[7,8]],3]]
+[[[[2,6],[5,0]],5],[[3,[5,4]],[[2,3],[8,6]]]]
+[[4,[[1,3],[1,3]]],[[[5,1],2],[[7,3],[9,6]]]]
+[[8,[6,[0,0]]],[[[4,4],9],[6,2]]]
+[[9,7],7]
+[[[3,1],[[0,3],[5,2]]],3]
+[[1,5],[4,[0,[3,6]]]]
+[[[[4,9],[6,5]],[8,4]],2]
+[[[7,[1,5]],4],[[3,[4,6]],[7,[4,3]]]]
+[[[0,[5,7]],[[8,7],[2,6]]],[[4,5],5]]
+[[[2,3],[[9,5],[9,3]]],[[[2,5],9],[[9,1],8]]]
+[[[[4,4],4],[[4,0],9]],[[[5,3],1],[3,[7,6]]]]
diff --git a/2021/day18/main.go b/2021/day18/main.go
new file mode 100644
index 0000000..098fe46
--- /dev/null
+++ b/2021/day18/main.go
@@ -0,0 +1,149 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToStringSlice()
+
+	var build *SNum
+	for i := range inp {
+		wrk, _ := ParseSNum(inp[i])
+		if build == nil {
+			build = wrk
+		} else {
+			build = build.add(wrk)
+		}
+	}
+	fmt.Println(build)
+	v := build.needsExplode(0)
+	fmt.Println("Needs Explode:", v)
+	v.explode()
+	fmt.Println(build)
+
+	/*
+		full := inp[0]
+		for i := 1; i < len(inp); i++ {
+			full = fmt.Sprintf("[%s,%s]", full, inp[i])
+		}
+	*/
+}
+
+type SNum struct {
+	parent, left, right *SNum
+	regular             bool
+	value               int
+}
+
+// ParseSNum returns an SNum and what's left of inp
+// after it was produced
+func ParseSNum(inp string) (*SNum, string) {
+	// inp should always start with either a number or a '['
+	var rest string
+	s := SNum{}
+	if inp[0] == '[' {
+		s.regular = false
+		s.left, rest = ParseSNum(inp[1:])
+		s.right, rest = ParseSNum(rest[1:])
+		s.left.parent = &s
+		s.right.parent = &s
+		return &s, rest[1:]
+	} else {
+		s.regular = true
+		var num []byte
+		for i := range inp {
+			if inp[i] >= '0' && inp[i] <= '9' {
+				num = append(num, inp[i])
+			} else {
+				s.value = h.Atoi(string(num))
+				return &s, inp[i:]
+			}
+		}
+	}
+	return &s, rest
+}
+
+func (s *SNum) needsExplode(depth int) *SNum {
+	if depth == 4 && !s.regular {
+		return s
+	}
+	if s.regular {
+		return nil
+	}
+	if tst := s.left.needsExplode(depth + 1); tst != nil {
+		return tst
+	} else if tst := s.right.needsExplode(depth + 1); tst != nil {
+		return tst
+	}
+	return nil
+}
+
+func (s *SNum) explode() {
+	if s.parent == nil {
+		return
+	}
+	s.parent.addToRegularRightOf(s.right.value, s)
+	s.parent.addToRegularLeftOf(s.left.value, s)
+}
+
+func (s *SNum) addToRegularLeftOf(v int, c *SNum) {
+	if s.right.regular {
+		s.right.value += v
+	} else {
+		if s.right != nil && s.right == c {
+			r := s.left.findRightmostRegular()
+			if r != nil {
+				r.value += v
+			}
+		} else if s.left != nil && s.left == c {
+			s.parent.addToRegularLeftOf(v, s)
+		}
+	}
+}
+
+func (s *SNum) addToRegularRightOf(v int, c *SNum) {
+	if s.left.regular {
+		s.left.value += v
+	} else if s.left != nil && s.left == c {
+		l := s.right.findLeftmostRegular()
+		if l != nil {
+			l.value += v
+		}
+	} else if s.right != nil && s.right == c {
+		s.parent.addToRegularRightOf(v, s)
+	}
+}
+
+func (s *SNum) contains(n *SNum) bool {
+	return s == n || s.left.contains(n) || s.right.contains(n)
+}
+
+func (s *SNum) findRightmostRegular() *SNum {
+	if s.regular {
+		return s
+	}
+	return s.right.findRightmostRegular()
+}
+func (s *SNum) findLeftmostRegular() *SNum {
+	if s.regular {
+		return s
+	}
+	return s.left.findLeftmostRegular()
+}
+
+func (s *SNum) add(n *SNum) *SNum {
+	return &SNum{
+		left:  s,
+		right: n,
+	}
+}
+
+func (s SNum) String() string {
+	if s.regular {
+		return fmt.Sprintf("%d", s.value)
+	}
+	return fmt.Sprintf("[%s,%s]", s.left, s.right)
+}
diff --git a/2021/day18/main.go.stringparse b/2021/day18/main.go.stringparse
new file mode 100644
index 0000000..bb2b153
--- /dev/null
+++ b/2021/day18/main.go.stringparse
@@ -0,0 +1,58 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToStringSlice()
+	build := inp[0]
+	for _, v := range inp[1:] {
+		build = fmt.Sprintf("[%s,%s]", build, v)
+	}
+
+	// Keep on steppin' until no change happens
+	var wrk string
+	var done bool
+	for !done {
+		wrk = step(build)
+		done = wrk == build
+		build = wrk
+	}
+	fmt.Println(wrk)
+}
+
+var steps int
+
+func step(inp string) string {
+	steps++
+	// Find the first number that needs to explode.
+	wrk := explode(inp)
+	if wrk != inp {
+		return wrk
+	}
+	// Nothing exploded, look for a split.
+	return split(inp)
+}
+
+func explode(inp string) string {
+	var depth int
+	for i := range inp {
+		if inp[i] == '[' {
+			if depth == 4 {
+				// Explode the leftmost pair from here
+
+			}
+			depth++
+		} else if inp[i] == ']' {
+			depth--
+		}
+	}
+}
+
+func split(inp string) string {
+
+	return inp
+}
diff --git a/2021/day18/testinput b/2021/day18/testinput
new file mode 100644
index 0000000..93e9d14
--- /dev/null
+++ b/2021/day18/testinput
@@ -0,0 +1,7 @@
+[1,2]
+[[1,2],3]
+[9,[8,7]]
+[[1,9],[8,5]]
+[[[[1,2],[3,4]],[[5,6],[7,8]]],9]
+[[[9,[3,8]],[[0,9],6]],[[[3,7],[4,9]],3]]
+[[[[1,3],[5,3]],[[1,3],[8,7]]],[[[4,9],[6,9]],[[8,2],[7,3]]]]
diff --git a/helpers/helpers.go b/helpers/helpers.go
index eda7a3e..ec8e9b7 100644
--- a/helpers/helpers.go
+++ b/helpers/helpers.go
@@ -148,7 +148,7 @@ func Atoi(i string) int {
 	var ret int
 	var err error
 	if ret, err = strconv.Atoi(i); err != nil {
-		log.Fatal("Invalid Atoi")
+		log.Fatal("Invalid Atoi:", i)
 	}
 	return ret
 }