A16300 | $Line Trip$

时间限制1s

内存限制256MB

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题目描述

There is a road, which can be represented as a number line. You are located in the point $0$ of the number line, and you want to travel from the point $0$ to the point $x$ , and back to the point $0$ . You travel by car, which spends $1$ liter of gasoline per $1$ unit of distance travelled. When you start at the point $0$ , your car is fully fueled (its gas tank contains the maximum possible amount of fuel). There are $n$ gas stations, located in points $a_1, a_2, \dots, a_n$ . When you arrive at a gas station, you fully refuel your car. Note that you can refuel only at gas stations, and there are no gas stations in points $0$ and $x$ . You have to calculate the minimum possible volume of the gas tank in your car (in liters) that will allow you to travel from the point $0$ to the point $x$ and back to the point $0$ .

The first line contains one integer $t$ ( $1 \le t \le 1000$ ) — the number of test cases. Each test case consists of two lines: - the first line contains two integers $n$ and $x$ ( $1 \le n \le 50$ ; $2 \le x \le 100$ ); - the second line contains $n$ integers $a_1, a_2, \dots, a_n$ ( $0 < a_1 < a_2 < \dots < a_n < x$ ).

For each test case, print one integer — the minimum possible volume of the gas tank in your car that will allow you to travel from the point $0$ to the point $x$ and back.

输入 #1

输出 #1

4
3
7

C++ 编辑器

输入

输出