Freshman's Database

input/code.cpp: In function 'int main()':
input/code.cpp:13:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
  freopen("cases.txt", "r", stdin);
  ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;
string s;

int arr[1000000] = {0};
bool visited[1000000] = {false};

int main() {
	freopen("cases.txt", "r", stdin);
	std::ios::sync_with_stdio(false);
	int n, r;
	r = 0;
	cin >> n;

	for (int i = 0; i < n; i++) {
		int num;
		cin >> num;
		arr[i] = num - 1;
	}

	for (int i = 0; i < n; i++) {
		if (visited[i] == false) {
			int next = i;
			int nextNext = i;

			do {
				next = arr[next];
				nextNext = arr[arr[nextNext]];
			} while ((next != nextNext));

			if (visited[next] == false) {
				r += 1;
			}

			
			int endPoint = next;
			do {
				visited[next] = true;
				next = arr[next];
			} while (next != endPoint && visited[next] == false);

		}
	}

	cout << r << endl;
	
	return 0;
}

Test 1

Verdict: RUNTIME ERROR

Test 2

Verdict: RUNTIME ERROR

Test 3

Verdict: RUNTIME ERROR

Test 4

Verdict: RUNTIME ERROR

Test 5

Verdict: RUNTIME ERROR

Test 6

Verdict: RUNTIME ERROR

Test 7

Verdict: RUNTIME ERROR

Test 8

Verdict: RUNTIME ERROR

Test 9

Verdict: RUNTIME ERROR

Test 10

Verdict: RUNTIME ERROR