Question 7
A subset S of vertices in an undirected graph G is half-independent if each vertex in S is adjacent to at most one other vertex in S. Is it true that finding the size of the largest half-independent set of vertices in a given undirected graph is NP-hard?
Yes, this can be shown by a reduction from the standard maximum independent set problem.
Yes, and this can be shown by reducing the half-independent set problem to the standard maximum independent set problem.
No, the problem of finding a largest half-independent set of vertices is in P since it can be reduced to the problem of finding a maximum matching.