There are two types of professional wrestlers: “baby faces” (“good guys”) and “heels” (“bad guys”). Between any pair of professional wrestlers, there may or may not be a rivalry. Suppose we have n professional wrestlers and we have a list of r pairs of wrestlers for which there are rivalries.

Required:

Give an O (n+r) time algorithm that determines whether it is possible to designate some of the wrestlers as baby faces and the remainder as heels such that each rivalry is between a baby face and a heel. If it is possible to perform such a designation, your algorithm should produce it.