Generate 1 and 0 with equal probability

Problem:
Given a function “f” in which 0 occurs with probability 0.4 and 1 occurs with probability 0.6. Using function “f” deduce a new function “f1” such that both 0 and 1 occurs with probability 0.5.

Solution:
Run the function f() two times. The possible outcomes are

00 with probability 0.4*0.4

11 with probability 0.6*0.6

01 with probability 0.4*0.6

10 with probability 0.6*0.4

Notice that the probabilities for 01 and 10 are the same. So create a new function f1() such that

f1():
   first = f()
   second = f()
   if (first == 0 and second == 0) or (first == 1 or second == 1):

      discard and run again
   else: 
      if first == 0 and second == 1: return 0
      else: return 1

Complexity:

time - O(1)
space - O(1)

Links and credits:
http://www.geeksforgeeks.org/amazon-interview-set-64-campus-sde/