This question is from exercise in my book Dynamic Programming for Coding Interviews (Question: 1.2, Page-5)

**Question:** Given an array, arr of integers, write a recursive function that add sum of all the previous numbers to each index of the array. For example, if the input array is

{1, 2, 3, 4, 5, 6}

then your function should update the array to

{1, 3, 6, 10, 15, 21}