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5086：Revenge of Segment Tree

题目描述
In computer science, a segment tree is a tree data structure for storing intervals, or segments. It allows querying which of the stored segments contain a given point. It is, in principle, a static structure; that is, its content cannot be modified once the structure is built. A similar data structure is the interval tree.
A segment tree for a set I of n intervals uses O(n log n) storage and can be built in O(n log n) time. Segment trees support searching for all the intervals that contain a query point in O(log n + k), k being the number of retrieved intervals or segments.
---Wikipedia

Today, Segment Tree takes revenge on you. As Segment Tree can answer the sum query of a interval sequence easily, your task is calculating the sum of the sum of all continuous sub-sequences of a given number sequence.
输入解释
The first line contains a single integer T, indicating the number of test cases.

Each test case begins with an integer N, indicating the length of the sequence. Then N integer Ai follows, indicating the sequence.

[Technical Specification]
1. 1 <= T <= 10
2. 1 <= N <= 447 000
3. 0 <= Ai <= 1 000 000 000
输出解释
For each test case, output the answer mod 1 000 000 007.
输入样例 
2
1
2
3
1 2 3
输出样例 
2
20
提示
For the second test case, all continuous sub-sequences are [1], [2], [3], [1, 2], [2, 3] and [1, 2, 3]. So the sum of the sum of the sub-sequences is 1 + 2 + 3 + 3 + 5 + 6 = 20.
Huge input, faster I/O method is recommended. And as N is rather big, too straightforward algorithm (for example, O(N^2)) will lead Time Limit Exceeded.
And one more little helpful hint, be careful about the overflow of int.
来自杭电HDUOJ的附加信息
Recommend heyang
该题目是Virtual Judge题目，来自 杭电HDUOJ
题目来源 BestCoder Round #16
源链接： HDU-5086
最后修改于 2020-10-25T23:19:40+00:00 由爬虫自动更新
共提交 0 次
通过率 --%
时间上限 内存上限
4000/2000MS(Java/Others) 32768/32768K(Java/Others)