30分树状数组求助

#include<bits/stdc++.h>
using namespace std;
inline int read()
{
    int x=0,t=1;char ch=getchar();
    while((ch<'0'||ch>'9')&&ch!='-')ch=getchar();
    if(ch=='-')t=-1,ch=getchar();
    while(ch<='9'&&ch>='0')x=x*10+ch-48,ch=getchar();
    return x*t;
}
int n,tree[500005],a[500005],m,b[500005];
long long ans;
inline int kth(int num){
    return lower_bound(b+1,b+m+1,num)-b;//位置 
}
inline void add(register int x,int num){
    for(;x<=n;x+=x&(-x))tree[x]+=num;
}
inline int query(register int x){
    int num=0;for(;x;x-=x&(-x))num+=tree[x];return num;
}
int main(){
    n=read();
    for(register int i=1;i<=n;i++){
        a[i]=read();
        b[i]=a[i];
    }
    sort(b+1,b+n+1);
    m=unique(b+1,b+1+n)-(b+1);
    for(register int i=1;i<=n;i++){
        add(kth(a[i]),1);
        ans+=kth(a[i])-(query(kth(a[i])-1))-1;
    }
    cout<<ans;
    return 0;
}

离散化的树状数组 30分求助