Submission #1224762

#	Time	Username	Problem	Language	Result	Execution time	Memory
1224762		chinhhoang	Mountains (NOI20_mountains)	C++20	100 / 100	107 ms	21704 KiB

Mountains

#include <bits/stdc++.h>
using namespace std;
int FT[3000002];
void updateFT(int i,int val){
    while(i<300000){
        FT[i]+=val;
        i+=i&-i;
    }
}
int getFT(int i){
    int s=0;
    while(i>0){
        s+=FT[i];
        i-=i&-i;
    }
    return s;
}
int main(){
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int n;
    cin>>n;
    vector<long long>a(n+1,0),val,pre(n+1,0),suf(n+1,0);
    for(int i=1;i<=n;i++)cin>>a[i],val.push_back(a[i]);
    sort(val.begin(),val.end());
    val.erase(unique(val.begin(),val.end()),val.end());
    for(int i=1;i<=n;i++)a[i]=int(lower_bound(val.begin(),val.end(),a[i])-val.begin())+1;
    for(int i=1;i<=n;i++)pre[i]=getFT(a[i]-1),updateFT(a[i],1);
    memset(FT,0,sizeof(FT));
    for(int i=n;i>=1;i--)suf[i]=getFT(a[i]-1),updateFT(a[i],1);
    long long ans=0;
    for(int i=1;i<=n;i++)ans+=pre[i]*suf[i];
    cout<<ans;
    return 0;
}

• Subtask 1: 2 / 2
• Subtask 2: 4 / 4
• Subtask 3: 9 / 9
• Subtask 4: 36 / 36
• Subtask 5: 28 / 28
• Subtask 6: 9 / 9
• Subtask 7: 12 / 12