Given two character strings s1 and s2. Write a Pthread program to find out the number of substrings, in string s1, that is exactly the same as s2. For example, suppose number_substring(s1, s2) implements the function, then number_substring(abcdab, ab) = 2, number_substring(aaa, a) = 3, number_substring(abac, bc) = 0. The size of s1 and s2 (n1 and n2) as well as their data are input by users. Assume that n1 mod NUM_T HREADS = 0 and n2 < n1/NUM_T HREADS.