Codeforces Round 889 (Div. 2)
A
Dalton the Teacher
Codeforces
800
原题
←B →
翻译中…

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 $n$.

翻译中…

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.

翻译中…

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).

翻译中…

Input

翻译中…

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.

翻译中…

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

翻译中…

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.

翻译中…

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

翻译中…

Output

翻译中…

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

翻译中…

Note

翻译中…

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

翻译中…

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.

翻译中…

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.

翻译中…

样例

Input #1
5
2
2 1
3
1 2 3
5
1 2 5 4 3
4
1 2 4 3
10
10 2 1 3 6 5 4 7 9 8
Output #1
0
2
2
1
1
InputCopy OutputCopy
题目信息
题号
1855A
时间限制
1 s
内存限制
256 MB
标签
贪心
数学

题面与样例版权归 Codeforces 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。