I have tried using bucket search( N*sqrt(N)) and segment tree based search( N*log(N)), but still only get AC in 0.1s

Anyone can shed some light on this? I have seen someone mentioned mergsort, is this the point?

Well, I've also tried merge sort approach(use iterative mergesort instead of recursive), but still only get AC in 0.078s

what's the point to boost it into 0.015s?

Anyone can shed some light?

Thanks a lot!