Write a function, largest_third(a), that computes the sum of the len(a)//3 of the largest values in the list a.

please see the attached picture.

Write a function, largest_third(a), that computes the sum of the len(a)//3 of the largest values in the list a. For simplicity, you may assume that the numbers in the list a are all distinct and that the list a has at least 3 elements.

 your goal is to design and implement solutions that are as fast as possible, and to analyze these solutions as well.