제출 #1173757

#제출 시각아이디문제언어결과실행 시간메모리
1173757ezzzayMountains (NOI20_mountains)C++20
22 / 100
117 ms4356 KiB
#include<bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define pb push_back
#define int long long
const int N=4e5;
int a[N];
int ps[N];
int sf[N];
void upps(int idx, int val){
    while(idx<N){
        ps[idx]+=val;
        idx+= idx & -idx;
    }
}
void upsf(int idx, int val){
    while(idx<N){
        sf[idx]+=val;
        idx+= idx & -idx;
    }
}
int fnsf(int idx){
    int s=0;
    while(idx>0){
        s+=sf[idx];
        idx-= idx &-idx;
    }
    return s;
}
int fnps(int idx){
    int s=0;
    while(idx>0){
        s+=ps[idx];
        idx-= idx &-idx;
    }
    return s;
}
signed main(){
    int n;
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a[i];
        a[i]+=2;
    }
    for(int i=1;i<=n;i++){
        upsf(a[i],1);
    }
    int ans=0;
    for(int i=1;i<=n;i++){
        ans+= ( fnsf(a[i]-1)) *((fnps(a[i]-1)));
       // cout<<(fnsf(N-1) - fnsf(a[i])) << " "<<(fnps(N-1)-(fnps(a[i])))<<endl;
        upsf(a[i],-1);
        upps(a[i],1);
    }
    cout<<ans;
}
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