(In Python): Write a function modExp(x, y, n) that computes and returns the value of x^y mod n. Use the fast modular exponentiation algorithm given in Figure 9.7.4 of the zyBook.

Figure 9.7.4: An iterative algorithm for fast modular exponentiation. Input: Positive integers x and y Output: xy mod n p 1 //p holds the partial result. s x Is holds the current a r y llr is used to compute the binary expansion of y While r> 0) If (r mod 2 1) p p s mod n s s-s mod n r r div 2 End-while Return(p)