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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5. 	int n; cin >> n;
  6. 	vector<int> arr(n+1);
  7.  
  8. 	for(int i = 1; i <= n; i++)
  9. 	cin >> arr[i];
  10.  
  11. 	unordered_map<int,int> hash;
  12. 	int cnt = 0;
  13. 	for(int i = 1; i <= n; i++){
  14. 		if(arr[i] > n)
  15. 		continue;
  16.  
  17. 		int req = arr[arr[arr[i]]];
  18. 		if(hash.find(req) != hash.end())
  19. 		cnt += hash[req];
  20.  
  21. 		hash[arr[arr[arr[i]]]]++;
  22. 	}
  23. 	cout << cnt;
  24. 	return 0;
  25. }
Success #stdin #stdout 0s 5316KB
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stdin
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4
4 2 1 2
stdout
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6
https://ideone.com/v1mIeK
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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