Print sequence of executions of processes. For example if in a system there are 3 processes i.e. P1, P2 and P3 and P1 depends on P2 and P3 while P2 depends on P3. Then the execution sequence will be: P3, P2, P1. Also if there is a cycle, program should exit.

Replace 'AB' with 'C' in a given string. Let's say if there is a srting "I am ABIndia living in ABCity.". The output of the program for this given string should be "I am CIndia living in CCity."