Random Number generation Issues

Question

This question was asked in my interview. random(0,1) is a function that generates integers 0 and 1 randomly. Using this function how would you design a function that takes two integers a,b as input and generates random integers including a and b.

I have No idea how to solve this.

Answer 1

We can do this easily by bit logic (E,g, a=4 b=10)

1. Calculate difference b-a (for given e.g. 6)
2. Now calculate ceil(log(b-a+1)(Base 2)) i.e. no of bits required to represent all numbers b/w a and b
3. now call random(0,1) for each bit. (for given example range will be b/w 000 - 111)
4. do step 3 till the number(say num) is b/w 000 to 110(inclusive) i.e. we need only 7 levels since b-a+1 is 7.So there are 7 possible states a,a+1,a+2,... a+6 which is b.
5. return num + a.