Submission #891122

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;

#define int int_fast64_t

signed main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr);

  int n; cin >> n;
  vector<int> v;
  copy_n(istream_iterator<int>(cin), n, back_inserter(v));

  auto friendly = [&](int x) {
    return (v[x]-1 != x &&
            v[v[x]-1]-1 == x);
  };
  int s=0;
  for (int i=0; i<n; ++i) s += friendly(i);
  cout << s/2 << '\n';
}

/*
 * Local variables:
 * compile-command:"g++ -D_GLIBCXX_DEBUG -g3 -ggdb3 -O0 -Wall -Wextra -std=c++14 b.cc -o b && for f in *.in; do echo \"--- $f -------------\"; ./b <$f; done"
 * end:
 */

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