codeforces#P1707B. Difference Array
Difference Array
Description
You are given an array $a$ consisting of $n$ non-negative integers. It is guaranteed that $a$ is sorted from small to large.
For each operation, we generate a new array $b_i=a_{i+1}-a_{i}$ for $1 \le i < n$. Then we sort $b$ from small to large, replace $a$ with $b$, and decrease $n$ by $1$.
After performing $n-1$ operations, $n$ becomes $1$. You need to output the only integer in array $a$ (that is to say, you need to output $a_1$).
The input consists of multiple test cases. The first line contains a single integer $t$ ($1\le t\le 10^4$) — the number of test cases. The description of the test cases follows.
The first line of each test case contains one integer $n$ ($2\le n\le 10^5$) — the length of the array $a$.
The second line contains $n$ integers $a_1,a_2,\dots,a_n$ ($0\le a_1\le \ldots\le a_n \le 5\cdot 10^5$) — the array $a$.
It is guaranteed that the sum of $n$ over all test cases does not exceed $2.5\cdot 10^5$, and the sum of $a_n$ over all test cases does not exceed $5\cdot 10^5$.
For each test case, output the answer on a new line.
Input
The input consists of multiple test cases. The first line contains a single integer $t$ ($1\le t\le 10^4$) — the number of test cases. The description of the test cases follows.
The first line of each test case contains one integer $n$ ($2\le n\le 10^5$) — the length of the array $a$.
The second line contains $n$ integers $a_1,a_2,\dots,a_n$ ($0\le a_1\le \ldots\le a_n \le 5\cdot 10^5$) — the array $a$.
It is guaranteed that the sum of $n$ over all test cases does not exceed $2.5\cdot 10^5$, and the sum of $a_n$ over all test cases does not exceed $5\cdot 10^5$.
Output
For each test case, output the answer on a new line.
Samples
5
3
1 10 100
4
4 8 9 13
5
0 0 0 8 13
6
2 4 8 16 32 64
7
0 0 0 0 0 0 0
81
3
1
2
0
Note
To simplify the notes, let $\operatorname{sort}(a)$ denote the array you get by sorting $a$ from small to large.
In the first test case, $a=[1,10,100]$ at first. After the first operation, $a=\operatorname{sort}([10-1,100-10])=[9,90]$. After the second operation, $a=\operatorname{sort}([90-9])=[81]$.
In the second test case, $a=[4,8,9,13]$ at first. After the first operation, $a=\operatorname{sort}([8-4,9-8,13-9])=[1,4,4]$. After the second operation, $a=\operatorname{sort}([4-1,4-4])=[0,3]$. After the last operation, $a=\operatorname{sort}([3-0])=[3]$.