Google Telephonic Round: (Result: Passed)

Q1: String Substitutor
Complete the following substitute() and register() functions for the following scenario.
Suppose we have following variables used in unix like environment:

USER= bob
HOME= /home/%USER% should be substituted as : /home/bob
ex2:
home/ %USER% -> /home/bob
Hello %USER% -> Hello bob!
ex3:
The user %USER% is at 50%% -> The user bob is at 50%

Complete following methods:
register(): To register the values of variable string
substitute(): Substitute values for variables that have been registered