CF1855A.Dalton the Teacher

Dalton is the teacher of a class with $n$ students, numbered from $1$ to $n$. The classroom contains $n$ chairs, also numbered from $1$ to $n$. Initially student $i$ is seated on chair $p_i$. It is guaranteed that $p_1,p_2,\dots, p_n$ is a permutation of length $n$.

A student is happy if his/her number is different from the number of his/her chair. In order to make all of his students happy, Dalton can repeatedly perform the following operation: choose two distinct students and swap their chairs. What is the minimum number of moves required to make all the students happy? One can show that, under the constraints of this problem, it is possible to make all the students happy with a finite number of moves.

A permutation of length $n$ is an array consisting of $n$ distinct integers from $1$ to $n$ in arbitrary order. For example, $[2,3,1,5,4]$ is a permutation, but $[1,2,2]$ is not a permutation ($2$ appears twice in the array), and $[1,3,4]$ is also not a permutation ($n=3$ but there is $4$ in the array).

达尔顿是一名有 $n$ 名学生的班级的教师，学生编号为 $1$ 到 $n$。教室中有 $n$ 把椅子，编号同样为 $1$ 到 $n$。初始时，学生 $i$ 坐在椅子 $p_i$ 上。保证 $p_1,p_2,\dots, p_n$ 是一个长度为 $n$ 的排列。

若一名学生的编号与其所坐椅子的编号不同，则该学生是快乐的。为了使所有学生都快乐，达尔顿可以反复执行以下操作：任选两名不同的学生，并交换他们所坐的椅子。问：使所有学生都快乐所需的最少操作次数是多少？可以证明，在本题约束下，总能通过有限次操作使所有学生都快乐。

长度为 $n$ 的排列是指由 $1$ 到 $n$ 这 $n$ 个互不相同的整数按任意顺序组成的数组。例如，$[2,3,1,5,4]$ 是一个排列，而 $[1,2,2]$ 不是排列（数组中 $2$ 出现了两次），$[1,3,4]$ 也不是排列（此时 $n=3$，但数组中出现了 $4$）。

Each test contains multiple test cases. The first line contains the number of test cases $t$ ($1 \le t \le 1000$). The description of the test cases follows.

The first line contains a single integer $n$ ($2 \le n \le 10^5$) — the number of students.

The second line contains $n$ integers $p_1, p_2, \ldots, p_n$ ($1 \le p_i \le n$) — $p_i$ denotes the initial chair of student $i$. It is guaranteed that $p$ is a permutation.

It is guaranteed that the sum of $n$ over all test cases does not exceed $10^5$.

每个测试包含多个测试用例。第一行包含测试用例的数量 $t$（$1 \le t \le 1000$）。随后是各测试用例的描述。

第一行包含一个整数 $n$（$2 \le n \le 10^5$）—— 表示学生的数量。

第二行包含 $n$ 个整数 $p_1, p_2, \ldots, p_n$（$1 \le p_i \le n$）—— 其中 $p_i$ 表示学生 $i$ 的初始座位号。保证 $p$ 是一个排列。

保证所有测试用例的 $n$ 之和不超过 $10^5$。

For each test case, output the minimum number of moves required.

对于每个测试用例，输出所需的最少移动次数。

In the first test case, both students are already happy, so Dalton can perform $0$ moves.

In the second test case, Dalton can swap the chairs of students $1$ and $2$ to get the array $[2, 1, 3]$. Then he can swap chairs of students $2$ and $3$ to get the array $[2, 3, 1]$. At this point all the students are happy, and he performed $2$ moves. It is impossible to perform the task with fewer moves.

In the third test case, by swapping the chairs of students $1$ and $2$ and then swapping the chairs of students $4$ and $5$, Dalton gets the array $[2, 1, 5, 3, 4]$ in $2$ moves.

在第一个测试用例中，两名学生都已经开心，因此 Dalton 可以执行 $0$ 次操作。

在第二个测试用例中，Dalton 可以交换学生 $1$ 和 $2$ 的座位，得到数组 $[2, 1, 3]$；接着再交换学生 $2$ 和 $3$ 的座位，得到数组 $[2, 3, 1]$。此时所有学生都已开心，他共执行了 $2$ 次操作。无法用少于 $2$ 次操作完成该任务。

在第三个测试用例中，Dalton 先交换学生 $1$ 和 $2$ 的座位，再交换学生 $4$ 和 $5$ 的座位，可在 $2$ 次操作内得到数组 $[2, 1, 5, 3, 4]$。