数据结构的实验，包换栈，链表，队列，各种排序(Data structure experiments, packet replacement stack, linked list, queue, sorting.)

segment tree 的简要实现，主要是面对与搜索的数据结构(Let us consider the following problem to understand Segment Trees. We have an array arr[0 . . . n-1]. We should be able to 1 Find the sum of elements from index l to r where 0 <= l <= r <= n-1 2 Change