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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4. #define int long long
  5.  
  6. const int N = 1e6 + 5;
  7. int n , sum;
  8. int a[N];
  9. int cnt[3];
  10.  
  11. main()
  12. {
  13.     ios::sync_with_stdio(0);
  14.     cin.tie(0);
  15.     cin >> n;
  16.     for(int i = 1 ; i <= n ; i++)
  17.     {
  18.         cin >> a[i];
  19.         sum += a[i];
  20.         if(a[i] % 2 == 0)
  21.             cnt[0]++;
  22.         else
  23.             cnt[1]++;
  24.     }
  25.     if(sum % 2 == 0)
  26.         cout << cnt[0] * (cnt[0] - 1) / 2
  27.               + cnt[1] * (cnt[1] - 1) / 2 << "\n";
  28.     else
  29.         cout << cnt[0] * cnt[1] << "\n";
  30.  
  31.  
  32.  
  33. }
Success #stdin #stdout 0.01s 5288KB
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https://ideone.com/Gx6g0O
language:
C++14 (gcc 8.3)
created:
16 days ago
visibility:
public

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