小心使得万年船，特别数据别样烦

首先我想说，很多题目真的是就差这么一点点 ，感觉自己哪里都没错，其实就是想不到一些特别的数据
B. Fixed Points
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

A permutation of length n is an integer sequence such that each integer from 0 to (n - 1) appears exactly once in it. For example, sequence [0, 2, 1] is a permutation of length 3 while both [0, 2, 2] and [1, 2, 3] are not.

A fixed point of a function is a point that is mapped to itself by the function. A permutation can be regarded as a bijective function. We’ll get a definition of a fixed point in a permutation. An integer i is a fixed point of permutation a0, a1, …, an - 1 if and only if ai = i. For example, permutation [0, 2, 1] has 1 fixed point and permutation [0, 1, 2] has 3 fixed points.

You are given permutation a. You are allowed to swap two elements of the permutation at most once. Your task is to maximize the number of fixed points in the resulting permutation. Note that you are allowed to make at most one swap operation.
Input

The first line contains a single integer n (1 ≤ n ≤ 105). The second line contains n integers a0, a1, …, an - 1 — the given permutation.
Output

Print a single integer — the maximum possible number of fixed points in the permutation after at most one swap operation.
Examples
Input

5
0 1 3 4 2

Output

3

#include <iostream>
#include <algorithm>
using namespace std;
int a[123456];
int main()
{
    int n;
    cin>>n;
    int i,cnt=0,t=0,flag=0;
    for(i=0;i<n;i++){
        cin>>a[i];
    }
    if (n==1) cnt=1;
    else{
    for(i=0;i<n;i++){
        t=a[i];
        if(a[i]==i)cnt++;
        else if(a[t]==i) flag=1;
    }
    if (flag==1) cnt=cnt+2;
    else cnt++;
    }
    cout <<cnt<<endl;
    return 0;
}

这个代码的具体意思就是说判断是不是有能交换的，交换后刚好满足有两个数再固定位置，+2或者+1

但是！
我忘记了要考虑不用交换的情况！！！
所以，思维的严密性非常重要