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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define int              long long int
  4. #define double           long double
  5. inline int power(int a, int b) {
  6.     int x = 1;
  7.     while (b) {
  8.         if (b & 1) x *= a;
  9.         a *= a;
  10.         b >>= 1;
  11.     }
  12.     return x;
  13. }
  14.  
  15.  
  16. const int M = 1000000007;
  17. const int N = 3e5+9;
  18. const int INF = 2e9+1;
  19. const int LINF = 2000000000000000001;
  20.  
  21. //_ ***************************** START Below *******************************
  22.  
  23.  
  24.  
  25. vector<int> a;
  26. void consistency(int n) {
  27. 	unordered_map<int,int> mp;
  28. 	for(int i=0; i<n; i++){
  29. 		mp[a[i]]++;
  30. 	}
  31. 	int ans = 0;
  32. 	for(auto& it : mp){
  33. 		if(it.second == 1){
  34. 			cout << -1 << endl;
  35. 			return;
  36. 		}
  37. 		ans += (it.second+3-1)/3;
  38. 	}
  39. 	cout << ans << endl;
  40. }
  41.  
  42. void solve() {
  43.  
  44.     int n;
  45.     cin >> n;
  46.     a.resize(n);
  47.     for(int i=0; i<n; i++) cin >> a[i];
  48.     consistency(n) ;
  49.  
  50. }
  51.  
  52.  
  53.  
  54.  
  55.  
  56. int32_t main() {
  57.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  58.  
  59.     int t = 1;
  60.     while (t--) {
  61.         solve();
  62.     }
  63.  
  64.     return 0;
  65. }
Success #stdin #stdout 0.01s 5288KB
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https://ideone.com/Tv3tAC
language:
C++14 (gcc 8.3)
created:
3 hours ago
visibility:
public

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