Does anyone know any online judge problem which deals with Volume of Union of Cuboids ?

I have solved closest pair and closest triplet problems using divide and conquer. I wonder if there is a problem ever asked which deals with finding closest quadruplet of points ( sum of distance between all pairs is minimum ) ? Also i want some efficient approach for solving similar problem for k-closest points.

Here is my code for the problem : http://ideone.com/UHbff

I got WA because on Codeforces judge for input 1 10000, its giving 10007 but on ideone and my system it gives 10008. Am i using any compiler version dependent statement ?

Can anyone explain the algorithm to solve area of union of circles problem( given n circles + centre and radius of each)

Thankyou