Find number of Employees Under every Employee

Given a dictionary that contains mapping of employee and his manager as a number of (employee, manager) pairs like below.

{ "A", "C" },
{ "B", "C" },
{ "C", "F" },
{ "D", "E" },
{ "E", "F" },
{ "F", "F" } 

In this example C is manager of A, 
C is also manager of B, F is manager 
of C and so on.

http://www.geeksforgeeks.org/find-number-of-employees-under-every-manager/