diff --git a/2017/day12/main.go b/2017/day12/main.go
new file mode 100644
index 0000000..8c22e42
--- /dev/null
+++ b/2017/day12/main.go
@@ -0,0 +1,98 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/mathutil"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	var ans int
+	if part == 1 {
+		ans = part1(util.ReadFile("./input.txt"))
+	} else {
+		ans = part2(util.ReadFile("./input.txt"))
+	}
+	fmt.Println("Output:", ans)
+}
+
+func part1(input string) int {
+	graph := makeGraphFromInput(input)
+
+	var count int
+	for k := range graph {
+		if dfsCanReachTarget(graph, k, 0, map[int]bool{}) {
+			count++
+		}
+	}
+
+	return count
+}
+
+func part2(input string) int {
+	graph := makeGraphFromInput(input)
+
+	allKeys := []int{}
+	for k := range graph {
+		allKeys = append(allKeys, k)
+	}
+
+	var groupCount int
+	// nodes that have been added to a group (that has been counted)
+	hasBeenGrouped := map[int]bool{}
+
+	for target := range graph {
+		if !hasBeenGrouped[target] {
+			// iterate through all graph nodes and check if they can be reached
+			for k := range graph {
+				// performance optimization: skip nodes that are already grouped
+				if k != target && !hasBeenGrouped[k] {
+					// if this group can reach the target, they're part of that group
+					if dfsCanReachTarget(graph, k, target, map[int]bool{}) {
+						hasBeenGrouped[k] = true
+					}
+				}
+			}
+			groupCount++
+		}
+	}
+
+	return groupCount
+}
+
+func dfsCanReachTarget(graph map[int][]int, entry int, target int, visited map[int]bool) bool {
+	// break infinite loops
+	if visited[entry] {
+		return false
+	}
+	visited[entry] = true
+
+	for _, child := range graph[entry] {
+		if child == target || dfsCanReachTarget(graph, child, target, visited) {
+			return true
+		}
+	}
+	// default to returning false
+	return false
+}
+
+func makeGraphFromInput(input string) map[int][]int {
+	lines := strings.Split(input, "\n")
+	graph := make(map[int][]int, len(lines))
+	for _, l := range lines {
+		parts := strings.Split(l, " <-> ")
+		ID := mathutil.StrToInt(parts[0])
+		for _, child := range strings.Split(parts[1], ", ") {
+			graph[ID] = append(graph[ID], mathutil.StrToInt(child))
+		}
+	}
+	return graph
+}
diff --git a/2017/day12/main_test.go b/2017/day12/main_test.go
new file mode 100644
index 0000000..8d2f1ef
--- /dev/null
+++ b/2017/day12/main_test.go
@@ -0,0 +1,54 @@
+package main
+
+import (
+	"testing"
+	"time"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+var example = `0 <-> 2
+1 <-> 1
+2 <-> 0, 3, 4
+3 <-> 2, 4
+4 <-> 2, 3, 6
+5 <-> 6
+6 <-> 4, 5`
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{"example", example, 6},
+		{"actual", util.ReadFile("input.txt"), 169},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_part2(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{"example", example, 2},
+		{"actual", util.ReadFile("input.txt"), 179},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			startTime := time.Now()
+			if got := part2(tt.input); got != tt.want {
+				t.Errorf("part2() = %v, want %v", got, tt.want)
+			}
+			t.Logf("Run time for %s: %v", tt.name, time.Since(startTime))
+		})
+	}
+}