Submission #71697810

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Source Code Expand

#include <iostream>
#include <algorithm>
#include <deque>
#include <vector>
#include <queue>
#include <cmath>
#include <unordered_set>
#include <unordered_map>
#include <map>
#include <set>
using namespace std;

int n;
int a[300001], parent[300001], len[300001];

int find(int x) {
	if (x == parent[x]) return x;
	return parent[x] = find(parent[x]);
}

void merge(int x, int y) {
	x = find(x);
	y = find(y);
	if (x == y) return;
	parent[y] = x;
	len[x] += len[y];
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		parent[i] = i;
		len[i] = 1;
	}
	
	for (int i = 1; i <= n; i++) {
		merge(i, a[i]);
	}
	
	long long ret = 0;

	for (int i = 1; i <= n; i++) {
		if (parent[i] == i) {
			ret += (long long)len[i] * (len[i] - 1) / 2;
		}
	}
	cout << ret;
}

Submission Info

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