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  1. #include<bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. #define int long long
  6.  
  7. int n;
  8. vector<int> a;
  9.  
  10. namespace sub1 { ///   TONGCHAN_trau
  11.     bool check() {
  12.         if (n <= 1000)       return true;
  13.         else return false;
  14.     }
  15.  
  16.     void solve() {
  17.         cerr << "run sub1: \n";     /// Nen viet 1 dong cerr de quan sat xem no co chay dc sub do hay ko?
  18.         int sum = 0;
  19.         for (int i = 1; i <= n; i++)
  20.             sum += a[i];
  21.         int ans = 0;
  22.         for (int i = 1; i <= n; i++) {
  23.             for (int j = i + 1; j <= n; j++) {
  24.                 if ((sum - a[i] - a[j]) % 2 == 0)
  25.                     ans++;
  26.             }
  27.         }
  28.         cout << ans;
  29.     }
  30. };
  31.  
  32. namespace sub2 {    /// TONGCHAN.cpp
  33.     bool check() {
  34.         return n > 1000;
  35.     }
  36.  
  37.     int c,l,sum;
  38.     void solve() {
  39.         cerr << "run sub2: \n";     /// Nen viet 1 dong cerr de quan sat xem no co chay dc sub do hay ko?
  40.         for (int i = 1; i <= n; i++) {
  41.             sum+=a[i];
  42.             if (a[i] % 2 == 0)      c++;
  43.             else l++;
  44.         }
  45.         if (sum % 2 == 0)
  46.             cout << (c*(c-1)/2) + (l*(l-1)/2);
  47.         else cout << c*l;
  48.     }
  49. };
  50.  
  51. signed main() {
  52.     freopen("TONGCHAN.INP", "r",stdin);
  53.     freopen("TONGCHAN.OUT", "w", stdout);
  54.     ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  55.     cin >> n;
  56.     a.resize(n + 1);
  57.     for (int i = 1; i <= n; i++)  {
  58.         cin >> a[i];
  59.     }
  60.  
  61.     /// return sub2::solve(), 0;        Neu nhu muon test tung sub
  62.  
  63.     if (sub1::check())          return sub1::solve(), 0;
  64.     if (sub2::check())          return sub2::solve(), 0;
  65. }
  66.  
Success #stdin #stdout #stderr 0.01s 5288KB
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stdin
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Standard input is empty
stdout
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Standard output is empty
stderr
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run sub1:
https://ideone.com/R9ygCp
language:
C++14 (gcc 8.3)
created:
15 days ago
visibility:
public

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