diff --git a/17/main.go b/17/main.go
new file mode 100644
index 0000000..cff5f6d
--- /dev/null
+++ b/17/main.go
@@ -0,0 +1,235 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+type cell struct {
+	x int // length
+	y int // width
+	z int // depth
+	w int // spissitude
+}
+
+type universe struct {
+	cells map[cell]bool
+	hyper bool // true: 4-dimensional; false: 3-dimensional
+}
+
+func makeNeighborsList(c cell, hyper bool) []cell {
+	cells := []cell{}
+	if hyper {
+		cells = append(cells, []cell{
+			// outward...?
+			// above
+			{x: c.x + 1, y: c.y + 1, z: c.z + 1, w: c.w + 1},
+			{x: c.x + 1, y: c.y, z: c.z + 1, w: c.w + 1},
+			{x: c.x + 1, y: c.y - 1, z: c.z + 1, w: c.w + 1},
+			{x: c.x, y: c.y + 1, z: c.z + 1, w: c.w + 1},
+			{x: c.x, y: c.y, z: c.z + 1, w: c.w + 1},
+			{x: c.x, y: c.y - 1, z: c.z + 1, w: c.w + 1},
+			{x: c.x - 1, y: c.y + 1, z: c.z + 1, w: c.w + 1},
+			{x: c.x - 1, y: c.y, z: c.z + 1, w: c.w + 1},
+			{x: c.x - 1, y: c.y - 1, z: c.z + 1, w: c.w + 1},
+
+			// same layer
+			{x: c.x + 1, y: c.y + 1, z: c.z, w: c.w + 1},
+			{x: c.x + 1, y: c.y, z: c.z, w: c.w + 1},
+			{x: c.x + 1, y: c.y - 1, z: c.z, w: c.w + 1},
+			{x: c.x, y: c.y + 1, z: c.z, w: c.w + 1},
+			{x: c.x, y: c.y, z: c.z, w: c.w + 1},
+			{x: c.x, y: c.y - 1, z: c.z, w: c.w + 1},
+			{x: c.x - 1, y: c.y + 1, z: c.z, w: c.w + 1},
+			{x: c.x - 1, y: c.y, z: c.z, w: c.w + 1},
+			{x: c.x - 1, y: c.y - 1, z: c.z, w: c.w + 1},
+
+			// below
+			{x: c.x + 1, y: c.y + 1, z: c.z - 1, w: c.w + 1},
+			{x: c.x + 1, y: c.y, z: c.z - 1, w: c.w + 1},
+			{x: c.x + 1, y: c.y - 1, z: c.z - 1, w: c.w + 1},
+			{x: c.x, y: c.y + 1, z: c.z - 1, w: c.w + 1},
+			{x: c.x, y: c.y, z: c.z - 1, w: c.w + 1},
+			{x: c.x, y: c.y - 1, z: c.z - 1, w: c.w + 1},
+			{x: c.x - 1, y: c.y + 1, z: c.z - 1, w: c.w + 1},
+			{x: c.x - 1, y: c.y, z: c.z - 1, w: c.w + 1},
+			{x: c.x - 1, y: c.y - 1, z: c.z - 1, w: c.w + 1},
+			// inward...?
+			// above
+			{x: c.x + 1, y: c.y + 1, z: c.z + 1, w: c.w - 1},
+			{x: c.x + 1, y: c.y, z: c.z + 1, w: c.w - 1},
+			{x: c.x + 1, y: c.y - 1, z: c.z + 1, w: c.w - 1},
+			{x: c.x, y: c.y + 1, z: c.z + 1, w: c.w - 1},
+			{x: c.x, y: c.y, z: c.z + 1, w: c.w - 1},
+			{x: c.x, y: c.y - 1, z: c.z + 1, w: c.w - 1},
+			{x: c.x - 1, y: c.y + 1, z: c.z + 1, w: c.w - 1},
+			{x: c.x - 1, y: c.y, z: c.z + 1, w: c.w - 1},
+			{x: c.x - 1, y: c.y - 1, z: c.z + 1, w: c.w - 1},
+
+			// same layer
+			{x: c.x + 1, y: c.y + 1, z: c.z, w: c.w - 1},
+			{x: c.x + 1, y: c.y, z: c.z, w: c.w - 1},
+			{x: c.x + 1, y: c.y - 1, z: c.z, w: c.w - 1},
+			{x: c.x, y: c.y + 1, z: c.z, w: c.w - 1},
+			{x: c.x, y: c.y, z: c.z, w: c.w - 1},
+			{x: c.x, y: c.y - 1, z: c.z, w: c.w - 1},
+			{x: c.x - 1, y: c.y + 1, z: c.z, w: c.w - 1},
+			{x: c.x - 1, y: c.y, z: c.z, w: c.w - 1},
+			{x: c.x - 1, y: c.y - 1, z: c.z, w: c.w - 1},
+
+			// below
+			{x: c.x + 1, y: c.y + 1, z: c.z - 1, w: c.w - 1},
+			{x: c.x + 1, y: c.y, z: c.z - 1, w: c.w - 1},
+			{x: c.x + 1, y: c.y - 1, z: c.z - 1, w: c.w - 1},
+			{x: c.x, y: c.y + 1, z: c.z - 1, w: c.w - 1},
+			{x: c.x, y: c.y, z: c.z - 1, w: c.w - 1},
+			{x: c.x, y: c.y - 1, z: c.z - 1, w: c.w - 1},
+			{x: c.x - 1, y: c.y + 1, z: c.z - 1, w: c.w - 1},
+			{x: c.x - 1, y: c.y, z: c.z - 1, w: c.w - 1},
+			{x: c.x - 1, y: c.y - 1, z: c.z - 1, w: c.w - 1},
+		}...)
+	}
+
+	// "normal" space
+	cells = append(cells, []cell{
+		// above
+		{x: c.x + 1, y: c.y + 1, z: c.z + 1, w: c.w},
+		{x: c.x + 1, y: c.y, z: c.z + 1, w: c.w},
+		{x: c.x + 1, y: c.y - 1, z: c.z + 1, w: c.w},
+		{x: c.x, y: c.y + 1, z: c.z + 1, w: c.w},
+		{x: c.x, y: c.y, z: c.z + 1, w: c.w},
+		{x: c.x, y: c.y - 1, z: c.z + 1, w: c.w},
+		{x: c.x - 1, y: c.y + 1, z: c.z + 1, w: c.w},
+		{x: c.x - 1, y: c.y, z: c.z + 1, w: c.w},
+		{x: c.x - 1, y: c.y - 1, z: c.z + 1, w: c.w},
+
+		// same layer
+		{x: c.x + 1, y: c.y + 1, z: c.z, w: c.w},
+		{x: c.x + 1, y: c.y, z: c.z, w: c.w},
+		{x: c.x + 1, y: c.y - 1, z: c.z, w: c.w},
+		{x: c.x, y: c.y + 1, z: c.z, w: c.w},
+		// <-- original cell
+		{x: c.x, y: c.y - 1, z: c.z, w: c.w},
+		{x: c.x - 1, y: c.y + 1, z: c.z, w: c.w},
+		{x: c.x - 1, y: c.y, z: c.z, w: c.w},
+		{x: c.x - 1, y: c.y - 1, z: c.z, w: c.w},
+
+		// below
+		{x: c.x + 1, y: c.y + 1, z: c.z - 1, w: c.w},
+		{x: c.x + 1, y: c.y, z: c.z - 1, w: c.w},
+		{x: c.x + 1, y: c.y - 1, z: c.z - 1, w: c.w},
+		{x: c.x, y: c.y + 1, z: c.z - 1, w: c.w},
+		{x: c.x, y: c.y, z: c.z - 1, w: c.w},
+		{x: c.x, y: c.y - 1, z: c.z - 1, w: c.w},
+		{x: c.x - 1, y: c.y + 1, z: c.z - 1, w: c.w},
+		{x: c.x - 1, y: c.y, z: c.z - 1, w: c.w},
+		{x: c.x - 1, y: c.y - 1, z: c.z - 1, w: c.w},
+	}...)
+
+	return cells
+}
+
+func checkNeighbors(u universe, c cell) bool {
+	sum := 0
+	for _, c := range makeNeighborsList(c, u.hyper) {
+		if u.cells[c] {
+			sum = sum + 1
+		}
+	}
+	if sum == 3 {
+		return true
+	} else if u.cells[c] && sum == 2 {
+		return true
+	}
+	return false
+}
+
+func step(old universe) universe {
+	new := universe{
+		cells: make(map[cell]bool, len(old.cells)),
+		hyper: old.hyper,
+	}
+	cellsToCheck := make([]cell, 0, len(old.cells)*80)
+	for c := range old.cells {
+		cellsToCheck = append(cellsToCheck, makeNeighborsList(c, old.hyper)...)
+	}
+	for _, c := range cellsToCheck {
+		if checkNeighbors(old, c) {
+			new.cells[c] = true
+		}
+	}
+	return new
+}
+
+func newUniverse(input []string, hyper bool) universe {
+	u := universe{
+		cells: make(map[cell]bool, len(input)),
+		hyper: hyper,
+	}
+
+	for i, r := range input {
+		for j, c := range r {
+			if c == '#' {
+				u.cells[cell{z: 0, x: i, y: j, w: 0}] = true
+			}
+		}
+	}
+
+	return u
+}
+
+func countActivesInUniverse(u universe) {
+	fmt.Println(len(u.cells))
+}
+
+func partOne() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	var input []string
+
+	for scanner.Scan() {
+		input = append(input, scanner.Text())
+	}
+
+	u := newUniverse(input, false)
+	u = step(u)
+	u = step(u)
+	u = step(u)
+	u = step(u)
+	u = step(u)
+	u = step(u)
+	countActivesInUniverse(u)
+}
+
+func partTwo() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	var input []string
+	for scanner.Scan() {
+		input = append(input, scanner.Text())
+	}
+
+	u := newUniverse(input, true)
+	u = step(u)
+	u = step(u)
+	u = step(u)
+	u = step(u)
+	u = step(u)
+	u = step(u)
+	countActivesInUniverse(u)
+}