Submission #1688818

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Source Code Expand

#include<bits/stdc++.h>
#define loop(i, a, b) for(int i = a; i < b; i++) 
#define rep(i, a) loop(i, 0, a)
using namespace std;
const int MOD = 1000000007;
const int inf = 1e8;
using vi = vector <int>;
using vvi = vector <vi>;
using vc = vector <char>;
using vvc = vector <vc>;
using vs = vector <string>;
using vvs = vector <vs>;
//g++ -std==c++14
//setprecision(10)
int n;
vi a;

int main(){
    cin >> n;
    a = vi(n);
    rep(i, n){
        cin >> a[i];
    }
    int cnt = 0;
    bool mada[n + 1] = {0};
    rep(i, n){
        if(a[a[i] - 1] == i + 1){
            if(mada[i + 1] == false && mada[a[a[i] - 1]] == false)
                cnt++;
            mada[i + 1] = true;
            mada[a[a[i] - 1]]= true;
        }
    }
    cout << cnt / 2 << endl;
}

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