Matching Random Motifs

http://rosalind.info/problems/rstr/

Given: A positive integer N≤100000, a number x between 0 and 1, and a DNA string s of length at most 10 bp.

Return: The probability that if N random DNA strings having the same length as s are constructed with GC-content x (see “Introduction to Random Strings”), then at least one of the strings equals s. We allow for the same random string to be created more than once.