If someone participated in that contest and has solved the fifth problem please kindly share your approach.
Well right now the contest problems are not visible but they will be open soon.
Here goes the contest link : https://my.newtonschool.co/course/yftr10ikg7/assignment/cqnqstjre9/dashboard/?tab=instructions
And I m describing the problem statement 
given two numbers L and X ’
( 0<=L,X <=1e9) you have to count the number of pairs (A,B) such that
A<=B<=L and gcd (A,B)=X
time limit was 2secs
Well Euler Toutient function striked me and we were supposed to calculate
phi(1) +phi(2) +…+ phi(L/X) but doing it in NlogN and O(N) space complexity gave me MLE.
So can anyone please help .