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A14425. Excellent Arrays

编程题 普及/提高-

题目描述

Let's call an integer array $a_1, a_2, \dots, a_n$ good if $a_i \neq i$ for each $i$ .

Let $F(a)$ be the number of pairs $(i, j)$ ( $1 \le i < j \le n$ ) such that $a_i + a_j = i + j$ .

Let's say that an array $a_1, a_2, \dots, a_n$ is excellent if:

- $a$ is good;
- $l \le a_i \le r$ for each $i$ ;
- $F(a)$ is the maximum possible among all good arrays of size $n$ .

Given $n$ , $l$ and $r$ , calculate the number of excellent arrays modulo $10^9 + 7$ .

输入格式

The first line contains a single integer $t$ ( $1 \le t \le 1000$ ) — the number of test cases.

The first and only line of each test case contains three integers $n$ , $l$ , and $r$ ( $2 \le n \le 2 \cdot 10^5$ ; $-10^9 \le l \le 1$ ; $n \le r \le 10^9$ ).

It's guaranteed that the sum of $n$ doesn't exceed $2 \cdot 10^5$ .

输出格式

For each test case, print the number of excellent arrays modulo $10^9 + 7$ .

输入输出样例

输入 #1
4
3 0 3
4 -3 5
42 -33 55
69 -42 146
输出 #1
4
10
143922563
698570404

说明/提示

In the first test case, it can be proven that the maximum $F(a)$ among all good arrays $a$ is equal to $2$ . The excellent arrays are:

1. $[2, 1, 2]$ ;
2. $[0, 3, 2]$ ;
3. $[2, 3, 2]$ ;
4. $[3, 0, 1]$ .
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