Freshman's Database

#include <iostream>

using namespace std;

int n;
int t[1000005];

int vis[1000005];

int res = 0;

void dfs(int s, int cc) {
	if (vis[s] != 0) {
		if (vis[s] == cc) {
			res++;
		}
		return;
	}
	vis[s] = cc;
	dfs(t[s], cc);
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cin >> n;
	for (int i = 1; i <= n; ++i) {
		int par;
		cin >> par;
		t[i] = par;
	}
	int cc = 1;
	for (int i = 1; i <= n; ++i) {
		if (vis[i] == 0) {
			dfs(i, cc++);
		}
	}
	cout << res << "\n";
	return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED