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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. #define ms(s,n) memset(s,n,sizeof(s))
  5. #define all(a) a.begin(),a.end()
  6. #define present(t, x) (t.find(x) != t.end())
  7. #define sz(a) int((a).size())
  8. #define FOR(i, a, b) for (int i = (a); i < (b); ++i)
  9. #define FORd(i, a, b) for (int i = (a) - 1; i >= (b); --i)
  10. #define pb push_back
  11. #define pf push_front
  12. #define fi first
  13. #define se second
  14. #define mp make_pair
  15.  
  16. typedef long long ll;
  17. typedef unsigned long long ull;
  18. typedef long double ld;
  19. typedef pair<int,int> pi;
  20. typedef vector<int> vi;
  21. typedef vector<pi> vii;
  22.  
  23. const int MOD = (int) 1e9+7;
  24. const int INF = (int) 1e9+1;
  25. inline ll gcd(ll a,ll b){ll r;while(b){r=a%b;a=b;b=r;}return a;}
  26. inline ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
  27.  
  28.  
  29. int main(){
  30. 	#ifndef ONLINE_JUDGE
  31. 	freopen("input.txt", "r", stdin);
  32. 	freopen("output.txt", "w", stdout);
  33. 	#endif
  34. 	int n;
  35. 	map<int, int> mp;
  36. 	cin >> n;
  37. 	for(int i = 0; i < n; i++){
  38. 		int x; cin >> x;
  39. 		mp[x]++;
  40. 	}
  41. 	ll ans = 0;
  42. 	for(auto it : mp){
  43. 		ans += 1ll * it.se * (it.se - 1) / 2;
  44. 	}
  45. 	cout << ans << endl;
  46. 	return 0;
  47. }
  48.  
Success #stdin #stdout 0s 5616KB
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https://ideone.com/zi2XQo
language:
C++14 (gcc 8.3)
created:
3 years ago
visibility:
public

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