How do you get from center Beijing to the Wall with public transportation without booking a tour?

There are two famous sections near the city.
If you want to go to the Mutianyu section, you can go to the Dongzhimen Bus Station to take bus 867 in the morning to reach there directly.
If you want to go to the Badaling section, you can go to the Deshengmen Bus Station to take bus 919 to reach Badaling directly.