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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4. #define ll long long
  5.  
  6. void solve(){
  7.     int n;
  8.     cin>>n;
  9.     vector<int>v(n),pref(n,0),suff(n,0);
  10.     for(int i=0;i<n;i++)cin>>v[i];
  11.     for(int i=0;i<n-1;i++){
  12.         for(int j=i+1;j<n;j++){
  13.             if(v[j]<v[i])pref[j]++;
  14.         }
  15.     }
  16.  
  17.     for(int i=n-1;i>0;i--){
  18.         for(int j=i-1;j>=0;j--){
  19.             if(v[j]<v[i])suff[j]++;
  20.         }
  21.     }
  22.  
  23.     int ans=0;
  24.     for(int i=1;i<n-1;i++){
  25.         ans+=pref[i]*suff[i];
  26.     }
  27.     cout<<ans<<"\n";
  28. }
  29.  
  30. int main(){
  31.     ios_base::sync_with_stdio(false);
  32.     cin.tie(NULL);
  33.     solve();
  34.     return 0;
  35. }
Success #stdin #stdout 0.01s 5308KB
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https://ideone.com/AY2MeG
language:
C++14 (gcc 8.3)
created:
14 days ago
visibility:
public

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