diff --git a/20210104/main.go b/20210104/main.go
new file mode 100644
index 0000000..5ef82bf
--- /dev/null
+++ b/20210104/main.go
@@ -0,0 +1,9 @@
+package main
+
+func main() {
+
+}
+
+func solution(s string) string {
+	return ""
+}
diff --git a/20210104/main_test.go b/20210104/main_test.go
new file mode 100644
index 0000000..272ca18
--- /dev/null
+++ b/20210104/main_test.go
@@ -0,0 +1,29 @@
+package main
+
+import "testing"
+
+func Test_solution(t *testing.T) {
+	type args struct {
+		s string
+	}
+	tests := []struct {
+		name string
+		args args
+		want string
+	}{
+		{
+			"test1",
+			args{
+				"aaaabbbbcccc",
+			},
+			"abccbaabccba",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := solution(tt.args.s); got != tt.want {
+				t.Errorf("solution() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}