Precise patterning of graphene is highly important for tailor-made and sophisticated two-dimensional nanoelectronic and optical devices. However, graphene-based heterostructures have been synthesized by delicate multi-step chemical vapor deposition methods, limiting preparation of versatile heterostructures. Here, we report single-step growth of graphene/amorphous carbon (a-C) heterostructures from a solid source of polystyrene through selective photo-crosslinking process. Graphene is successfully grown from neat polystyrene regions, while crosslinked polystyrene regions turn into a-C because of a large difference in their thermal stability. Since the electrical resistance of a-C is at least two orders of magnitude higher than that for graphene, the charge transport in graphene/a-C heterostructure occurs through the graphene area. Measurement of the quantum Hall effect in graphene/a-C lateral heterostructures clearly confirms the reliable quality of graphene and well-defined graphene/a-C interface. The ability to directly synthesize patterned graphene from polymer pattern opens up new possibilities for the preparation of versatile heterostructures.