You are given a graph G$.($Think$,$ G is huge.$)$ You are asked to build a suitable data structure from G that can help you efficiently answer the following queries on$-$demand:

input: a node v$,$ output all the nodes reachable from v$.$

Describe your data structure and how you will build it from G$.($Though there is no hard limit on the time to build your data structure as a function of G$\text{'}$s size, relatively inefficient solutions will get points deducted.$)$ How long does it take to build your data structure in terms of G$\text{'}$s size? Explain. Explain how your data structure is used to efficiently respond to a query and how long this takes.