Given a matrix mat with n columns, return a row vector v of length n, where every element in v is the product of the n-th column.
You cannot use MATLAB Prod() function
Example:
Input: mat = [ 1, 2, 3, 4;
5, 6, 7, 2;
2, 3, 4, 5]
Output: v = [10, 36, 84, 40]