Given a sequence of K elements, we can calculate its difference sequence by taking the difference between each pair of adjacent elements. For instance, the difference sequence of {5,6,3,9,1} is {65,36,93,19} = {1,3,6,10}. Formally, the difference sequence of the sequence a_{1}, a_{2}, ... , a_{k} is b_{1}, b_{2}, ... , b_{k1}, where b_{i} = a_{i+1}  a_{i}.
The derivative sequence of order N of a sequence A is the result of iteratively applying the above process N times. For example, if A = {5,6,3,9,1}, the derivative sequence of order 2 is: {5,6,3,9,1} > {1,3,6,10} > {31,6(3),106} = {4,9,16}.
You will be given a sequence a as a int[] and the order n. Return a int[] representing the derivative sequence of order n of a.
