diff --git a/2015/day11/main.go b/2015/day11/main.go
new file mode 100644
index 0000000..34beb37
--- /dev/null
+++ b/2015/day11/main.go
@@ -0,0 +1,82 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+
+	"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)
+
+	ans := passwordIncrementing(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+func passwordIncrementing(input string, part int) string {
+	pw := input
+	for !isValid(pw) {
+		pw = incrementString(pw)
+	}
+
+	if part == 1 {
+		return pw
+	}
+
+	pw = incrementString(pw)
+	for !isValid(pw) {
+		pw = incrementString(pw)
+	}
+
+	return pw
+}
+
+func incrementString(in string) string {
+	chars := strings.Split(in, "")
+	for i := len(chars) - 1; i >= 0; i-- {
+		if chars[i] == "z" {
+			// continue loop to carry "carry over the one"
+			chars[i] = "a"
+		} else {
+			asciiCode := cast.ToASCIICode(chars[i])
+			chars[i] = cast.ASCIIIntToChar(asciiCode + 1)
+			break
+		}
+	}
+	return strings.Join(chars, "")
+}
+
+func isValid(in string) bool {
+	rule1 := func(in string) bool {
+		for i := 2; i < len(in); i++ {
+			if in[i-2]+1 == in[i-1] && in[i-1]+1 == in[i] {
+				return true
+			}
+		}
+		return false
+	}
+
+	rule2 := func(in string) bool {
+		return !regexp.MustCompile("[iol]").MatchString(in)
+	}
+
+	rule3 := func(in string) bool {
+		pairs := map[string]bool{}
+		for i := 1; i < len(in); i++ {
+			if in[i-1] == in[i] {
+				pairs[in[i-1:i+1]] = true
+			}
+		}
+		return len(pairs) >= 2
+	}
+
+	return rule1(in) && rule2(in) && rule3(in)
+}
diff --git a/2015/day11/main_test.go b/2015/day11/main_test.go
new file mode 100644
index 0000000..0200af8
--- /dev/null
+++ b/2015/day11/main_test.go
@@ -0,0 +1,26 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_passwordIncrementing(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  string
+	}{
+		{"part1 actual", util.ReadFile("input.txt"), 1, "hxbxxyzz"},
+		{"part2 actual", util.ReadFile("input.txt"), 2, "hxcaabcc"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := passwordIncrementing(tt.input, tt.part); got != tt.want {
+				t.Errorf("passwordIncrementing() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}