Pigs

#include <iostream>
#include <fstream>
#include <map>
#include <set>
using namespace std;

void dfs(int start, map<int, set<int>> &adjSets, map<int, bool> &used) {

    used[start] = true;
    for (auto neighbour: adjSets[start]) {
        if (!used[neighbour]) {
            dfs(neighbour, adjSets, used);
        }
    }

}

int main() {
    ifstream file("input.txt");
    int n;
    file >> n;

    map<int, set<int>> adjSets;
    map<int, bool> used;

    for (int i = 0; i < n; i++) {
        int value;
        file >> value;
        adjSets[i].insert(value-1);
        adjSets[value-1].insert(i);
        used[i] = false;
    }

    int result = 0;
    for (int i = 0; i < n; i++) {
        if (!used[i]) {
            dfs(i, adjSets, used);
            result += 1;
        }
    }

    cout << result << endl;

    return 0;
}