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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. // 1
  24. // 4
  25. // 4 2 1 2
  26.  
  27.  
  28. //* Alternatve way : 
  29. //* freqMap = { 
  30. //*      x -> c1
  31. //* 	 y -> c2
  32. //* 	... -> ...
  33. //* }
  34.  
  35. //* Ans = (1 + 2 + 3 + ... c1-1)   +  (1 + 2+ ... c2-1)   +  ....
  36. //* 	ans = c1(c1-1)/2 + c2(c2-1)/2 
  37.  
  38. //* This is what we do each time with =>  
  39. //* 	ans += mp[val]	
  40. //* 	map[val]++
  41.  
  42.  
  43. vector<int> a;
  44. void consistency(int n) {
  45.  
  46. 	unordered_map<int,int> mp;
  47. 	int ans = 0;
  48.  
  49. 	for(int i=1; i<=n; i++){
  50. 		int val = a[a[a[i]]];
  51. 		if(mp.count(val)){
  52. 			ans += mp[val];
  53. 		}
  54.  
  55. 		mp[val]++;
  56. 	}
  57.  
  58. 	cout << ans << endl;
  59.  
  60. }
  61.  
  62. void solve() {
  63.  
  64.     int n;
  65.     cin >> n;
  66.     a.resize(n+1);
  67.     for(int i=1; i<=n; i++) cin >> a[i];
  68.     consistency(n) ;
  69.  
  70. }
  71.  
  72.  
  73.  
  74.  
  75.  
  76. int32_t main() {
  77.     ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  78.  
  79.     int t = 1;
  80.     cin >> t;
  81.     while (t--) {
  82.         solve();
  83.     }
  84.  
  85.     return 0;
  86. }
Success #stdin #stdout 0.01s 5260KB
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1
4
4 2 1 2
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https://ideone.com/FxyhCC
language:
C++14 (gcc 8.3)
created:
15 hours ago
visibility:
public

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