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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main(){
  5.     int n; cin >> n;
  6.     int ar[n+5];
  7.     for (int i = 1; i <= n; i++){
  8.         cin >> ar[i];
  9.     }
  10.  
  11.     map<int,int> freq;
  12.     for (int i = 1; i <= n; i++){
  13.         freq[ar[i]] += 1;
  14.     }
  15.  
  16.     //use a long long because it can store a bigger number
  17.     long long ans = 0, tot = n;
  18.  
  19.     /*
  20.     n = 5
  21.     1 1 2 2 3
  22.  
  23.     {{1: 2}, {2: 2}, {3: 1}}
  24.  
  25.     it = {3: 1}
  26.     it.first = 3
  27.     it.second = 1
  28.     */
  29.     for (auto it: freq){
  30.         int val = it.second;
  31.         ans += val*(tot-val);
  32.         tot -= val;
  33.     }
  34.  
  35.     cout << ans << endl;
  36. }
Success #stdin #stdout 0s 5288KB
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https://ideone.com/LPXvXR
language:
C++ (gcc 8.3)
created:
20 days ago
visibility:
public

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