信息中继

#include<iostream>
using namespace std;
const int N = 1010;
int a[N], b[N], p[N], s[N];
int find(int x)
{
    if(p[x] != x)p[x]  = find(p[x]);
    return p[x];
}
int main()
{
    int n;
    cin >> n;
    for(int i = 1; i <= n; i ++)a[i] = i;
    for(int i = 1; i <= n; i ++)
    {
        cin >> b[i];
    }
    int ans = 0;
    for(int i = 1; i <= n; i ++)p[i] = i, s[i] = 1; 
    for(int i = 1; i <= n; i ++)
    {
       int x = a[i], y = b[i];
       if(find(x) != find(y) && y != 0)
       {
           s[find(y)] += s[find(x)];
            p[find(x)] = find(y);
       }
    }
    for(int i = 1; i <= n; i ++)
    {
        if(b[i] == 0){
            int x = find(i);
            ans += s[x];
        }
    }
    cout << ans <<endl;
}