XOR Mixup (Codeforces 1698A)
Tags: Others, bitmasks

There is an array $$$a$$$ with $$$n-1$$$ integers. Let $$$x$$$ be the bitwise XOR of all elements of the array. The number $$$x$$$ is added to the end of the array $$$a$$$ (now it has length $$$n$$$), and then the elements are shuffled.You are given the newly formed array $$$a$$$. What is $$$x$$$? If there are multiple possible values of $$$x$$$, you can output any of them.

Input: The input consists of multiple test cases. The first line contains an integer $$$t$$$ ($$$1 \leq t \leq 1000$$$) — the number of test cases. The description of the test cases follows.The first line of each test case contains an integer $$$n$$$ ($$$2 \leq n \leq 100$$$) — the number of integers in the resulting array $$$a$$$.The second line of each test case contains $$$n$$$ integers $$$a_1, a_2, \ldots, a_n$$$ ($$$0 \le a_i \le 127$$$) — the elements of the newly formed array $$$a$$$.Additional constraint on the input: the array $$$a$$$ is made by the process described in the statement; that is, some value of $$$x$$$ exists.

Output: For each test case, output a single integer — the value of $$$x$$$, as described in the statement. If there are multiple possible values of $$$x$$$, output any of them.

Note: In the first test case, one possible array $$$a$$$ is $$$a=[2, 5, 4]$$$. Then $$$x = 2 \oplus 5 \oplus 4 = 3$$$ ($$$\oplus$$$ denotes the bitwise XOR), so the new array is $$$[2, 5, 4, 3]$$$. Afterwards, the array is shuffled to form $$$[4, 3, 2, 5]$$$.In the second test case, one possible array $$$a$$$ is $$$a=[1, 10, 6, 10]$$$. Then $$$x = 1 \oplus 10 \oplus 6 \oplus 10 = 7$$$, so the new array is $$$[1, 10, 6, 10, 7]$$$. Afterwards, the array is shuffled to form $$$[6, 1, 10, 7, 10]$$$.In the third test case, all elements of the array are equal to $$$6$$$, so $$$x=6$$$.In the fourth test case, one possible array $$$a$$$ is $$$a=[100, 100]$$$. Then $$$x = 100 \oplus 100 = 0$$$, so the new array is $$$[100, 100, 0]$$$. Afterwards, the array is shuffled to form $$$[100, 100, 0]$$$. (Note that after the shuffle, the array can remain the same.)

Sample Inputs:
4
4
4 3 2 5
5
6 1 10 7 10
6
6 6 6 6 6 6
3
100 100 0

Sample Outputs:
3
7
6
0

Solution (Python):
for i in range(int(input())):
    n = input()
    print(input().split()[0])

Solution (Python):
for s in [*open(0)][2::2]:
    print(s.split()[0])

Solution (Python):
for s in [*open(0)][2::2]:
    print(s.split()[0])