241. 楼兰图腾树状数组

Posted 2021-10-30 幽殇默

https://www.acwing.com/problem/content/243/

#include<bits/stdc++.h>
using namespace std;
const int N=1e5*2+10;
typedef long long int LL;
LL tr[N],up[N],down[N],a[N];
int n;
int lowbit(int x){return x&(-x);}
int add(int x,int c)
{
    for(int i=x;i<=n;i+=lowbit(i)) tr[i]+=c;
}
int sum(int x)
{
    int res=0;
    for(int i=x;i;i-=lowbit(i)) res+=tr[i];
    return res;
}
int main(void)
{
    cin>>n;
    for(int i=1;i<=n;i++) cin>>a[i];
    for(int i=1;i<=n;i++)
    {
        int y=a[i];
        down[i]=sum(y-1);
        up[i]=sum(n)-sum(y);
        add(y,1);
    }
    memset(tr,0,sizeof tr);
    LL res1=0,res2=0;
    for(int i=n;i;i--)
    {
        int y=a[i];
        res1+=up[i]*(sum(n)-sum(y));
        res2+=down[i]*(sum(y-1));
        add(y,1);
    }
    cout<<res1<<" "<<res2;
    return 0;
}