A de Bruijn sequence of order n on a size-k alphabet A is a cyclic sequence in which every possible length-n string on A occurs exactly once as a substring.

For a de Bruijn sequence of order n on a size-k alphabet $A$, we denote it by $B(k, n)$

A segment tree is a binary tree where each node represents an interval. Each node stores some property of its corresponding interval: like the maximum/minimum num, the sum of that interval.