Write a C++ function sum(n) that returns the sum of decimal digits of a positive integer n (e.g. sum(123) should return 6). Then write a function AllDifferent(a, na) that returns 1 if all components of the positive integer array a[0 .. na-1] have different sums of digits; otherwise it returns 0. E.g., the array a[ ] = {17, 22, 33, 41, 9} has all different sums of digits and AllDifferent(a, 5) must return 1.