VertexInComponent
VertexInComponent[g,{v1,v2,…},k]
gives the vertices with a directed path to at least one of v1, v2, … of at most length k.
VertexInComponent[g,{v1,v2,…},{k}]
gives the vertices at length exactly k.
VertexInComponent[{vw,…},…]
uses rules vw to specify the graph g.
Details

- VertexInComponent works for any directed graph object.
- VertexInComponent works with undirected graphs, directed graphs, multigraphs, and mixed graphs.

Examples
open allclose allScope (8)
VertexInComponent works with undirected graphs:
Use rules to specify the graph:
Use patterns to select a subset of vertices:
Find the in-component connected to a vertex by a path of at most length 2 in a graph:
VertexInComponent works with large graphs:
Properties & Relations (1)
Use VertexOutComponent to find the out-component for directed graphs:
Text
Wolfram Research (2010), VertexInComponent, Wolfram Language function, https://reference.wolfram.com/language/ref/VertexInComponent.html (updated 2020).
CMS
Wolfram Language. 2010. "VertexInComponent." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2020. https://reference.wolfram.com/language/ref/VertexInComponent.html.
APA
Wolfram Language. (2010). VertexInComponent. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/VertexInComponent.html