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  1. #include<bits/stdc++.h>
  2. #define f1(i, n) for(ll i=1;i<=n;++i)
  3. #define f0(i, n) for(ll i=0;i<n;++i)
  4. #define ull unsigned long long
  5. #define ll long long
  6. #define rev(a) reverse(a.begin(),a.end())
  7. #define all(x) x.begin(),x.end()
  8. #define so(A, n) sort(A+1, A+n+1)
  9. using namespace std;
  10. const int maxn = 2e5 + 1;
  11. ll A[maxn];
  12. int main()
  13. {
  14. 	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  15. 	int n;
  16. 	cin >> n;
  17. 	map<ll, ll> mp;
  18. 	map<pair<ll, ll>, bool> melody_mark;
  19. 	f1(i, n) {
  20. 		cin >> A[i];
  21. 		mp[A[i]]++;
  22. 	}
  23. 	int cnt = 0;
  24. 	for (int i = 1; i <= n; ++i) {
  25. 		for (int j = i + 1; j <= n; ++j) {
  26. 			if (!melody_mark[make_pair(min(A[i], A[j]), max(A[i], A[j]))]) cnt += mp[A[i] + A[j]];
  27. 			melody_mark[make_pair(min(A[i], A[j]), max(A[i], A[j]))] = true;
  28. 		}
  29. 	}
  30. 	cout << cnt;
  31.  
  32. 	return 0;
  33. }
  34.  
  35.  
Success #stdin #stdout 0s 5284KB
comments (?)
stdin 
3
-1 0 -1
stdout 
2
https://ideone.com/9l5ifR
Bài 4 - LHP 2024 - 2025
language:
C++14 (gcc 8.3)
created:
14 days ago
visibility:
public

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