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- #include <bits/stdc++.h>
- using namespace std;
- int B[100000], a[100000],n;
- int init()
- {
- cin>>n;
- for(int i=1;i<=n;i++) cin>>a[i];
- vector<int> v(a+1,a+n+1);
- sort(v.begin(),v.end());
- unique(v.begin(),v.end());
- for(int i=1;i<=n;i++) {int x= a[i]; a[i]= lower_bound(v.begin(),v.end(),x)-v.begin()+1;}
- }
- void upd(int v)
- {
- while(v<=n){
- B[v]++;
- v+=(v&-v);
- }
- }
- int get(int v)
- {
- int res=0;
- while(v>0){
- res+=B[v];
- v-=(v&-v);
- }
- return res;
- }
- int main(){
- int sult=0;
- init();
- //for(int i=1;i<=n;i++) cout<<a[i]<<' ';
- upd(a[n]);
- for(int i=n-1;i>=1;i--)
- {
- sult+= get(a[i]-1);
- upd(a[i]);
- }
- cout<<sult;
- }
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