Figure $1$: Communication network $G$ shown on the left. The lightly shaded nodes are the operators, the

dark shaded nodes are the spies, and the clear nodes are other nodes. The dashed edges form a set of links

that can be removed leading to the network on the right, where there is no directed path from any operator

to any spy$.$

$($a$)$ Describe the input and output of your algorithm.

$($b$)$ Describe your algorithm in pseudocode.

$($c$)$ Justify the correctness of your algorithm. Your justification does not need to be long or formal, just

convincing.

$($d$)$ Analyze the running time of your algorithm.