<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def running_apps(self):
 """Return a list of running user applications."""

        ps = self.adb_shell(RUNNING_APPS_CMD)
        if ps:
            return [line.strip().rsplit(' ', 1)[-1] for line in ps.splitlines() if line.strip()]
        return []