He used the Zone System of exposure and developing.
Yes, quite familiar with it (taught it for many years). Pre-visualizing the final print doesn't preclude having to do extensive darkroom work to get there...far from it. Typically (and sensibly), Adams aimed to get as much information as possible on the negative so he could have the freedom to emphasize what he wanted to in the final print. The only reason you need zone system at all is because of the limited latitude of film; if he could capture all the information inherent in a scene without resorting to "placing" zones (that is, making choices about what information would be included or not included in an exposure) or varying developer recipes, he would surely have done it.