Codility - Lesson 5 Prefix sums

Source Link:
https://codility.com/programmers/lessons/5-prefix_sums/

Some Notes:

There is a simple yet powerful technique that allows for the fast calculation of sums of elements in given slice (contiguous segments of array). Its main idea uses prefix sums which are defined as the consecutive totals of the first 0, 1, 2, . . . , n elements of an array. 

Similarly, we can calculate suffix sums, which are the totals of the k last values. Using prefix (or suffix) sums allows us to calculate the total of any slice of the array very quickly.