Make a fair coin from a biased coin

You are given a function foo() that represents a biased coin. When foo() is called, it returns 0 with 60% probability, and 1 with 40% probability. Write a new function that returns 0 and 1 with a 50% probability each. Your function should use only foo(), no other library method.

Solution: 
We know foo() returns 0 with 60% probability. How can we ensure that 0 and 1 are returned with a 50% probability? 
The solution is similar to this post. If we can somehow get two cases with equal probability, then we are done. We call foo() two times. Both calls will return 0 with a 60% probability. So the two pairs (0, 1) and (1, 0) will be generated with equal probability from two calls of foo(). Let us see how.
(0, 1): The probability to get 0 followed by 1 from two calls of foo() = 0.6 * 0.4 = 0.24 
(1, 0): The probability to get 1 followed by 0 from two calls of foo() = 0.4 * 0.6 = 0.24
So the two cases appear with equal probability. The idea is to return consider only the above two cases, return 0 in one case, return 1 in other case. For other cases [(0, 0) and (1, 1)], recur until you end up in any of the above two cases. 

The below program depicts how we can use foo() to return 0 and 1 with equal probability.  

Time Complexity: O(1)

Auxiliary Space: O(1)

References: 
https://en.wikipedia.org/wiki/Fair_coin#Fair_results_from_a_biased_coin
This article is compiled by Shashank Sinha and reviewed by GeeksforGeeks team.