P1966 火柴排队

Posted 2020-10-11 wang者归来

https://www.luogu.org/problem/show?pid=1966

求逆序对

用树状数组。

 

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<cstring>
#include<cmath>
using namespace std;//60fen
const int N=100009;
const long long P=99999997; 
struct node{
    int x;//数值 
    int w;//原来位置 
}A[N],B[N];
int n;
bool cmp(node a,node b)
{
    return a.x<=b.x;
}
int c[N],d[N];
int Add(int x)
{
    int ans=0;
    for(int i=x;i<=n;i+=i&(-i))
        c[i]=(c[i]+1)%P;
    for(int i=x;i>0;i-=i&(-i))
        ans=(ans+c[i])%P;
    return ans;
}
int main() 
{
//    freopen("match.in","r",stdin);
//    freopen("match.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&A[i].x);
        A[i].w=i;
    }
    for(int i=1;i<=n;i++)
    {
        scanf("%d",&B[i].x);
        B[i].w=i;
    }
    sort(A+1,A+1+n,cmp);
    sort(B+1,B+1+n,cmp);
    
    for(int i=1;i<=n;i++)
        d[A[i].w]=B[i].w;
    long long ans=0;
    for(int i=1;i<=n;i++)
    {
        ans=(ans+i-Add(d[i]))%P;
    } 
    cout<<ans;
    return  0;
}