bzoj3295 [Cqoi2011]动态逆序对

　　cdq分治。

　　代码

#include<cstdio>
#include<algorithm>
#define N 200010
#define lb(x) (x&-x)
using namespace std;
int n,b[N],a[N],id[N],ans[N],i,m,L[N],R[N],c[N];
long long Ans;
struct g{
    int v,typ;
}v[N];
bool cmp(g a,g b)
{
    return a.v<b.v;
}
void cc(int x,int w)
{
    while (x<=n)
    {
        c[x]+=w;
        x+=lb(x);
    }
}
int sum(int x)
{
    int ans=0;
    while (x)
    {
        ans+=c[x];
        x-=lb(x);
    }
    return ans;
}
void solve(int l,int r)
{
    int m,i,tot=0,cnt=0;
    if (l>=r) return;
    m=(l+r)>>1;
    for (i=l;i<=m;i++)
    {
        v[++tot].typ=0;
        v[tot].v=b[i];
    }
    for (i=m+1;i<=r;i++)
    {
        v[++tot].typ=i;
        v[tot].v=b[i];
    }
    sort(v+1,v+1+tot,cmp);
    for (i=tot;i>=1;i--)
    if (v[i].typ) 
    ans[v[i].typ]+=sum(id[v[i].v]);
    else
    cc(id[v[i].v],1);
    for (i=1;i<=tot;i++)
    if (v[i].typ==0)
    cc(id[v[i].v],-1);
    
    for (i=1;i<=tot;i++)
    if (v[i].typ) 
    ans[v[i].typ]+=cnt-sum(id[v[i].v]);
    else
    {
        cnt++;
        cc(id[v[i].v],1);
    }
    for (i=1;i<=tot;i++)
    if (v[i].typ==0)
    cc(id[v[i].v],-1);
    
    solve(l,m);
    solve(m+1,r);
}
int main()
{
    scanf("%d%d",&n,&m);
    for (i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
        id[a[i]]=i;
    }
    for (i=1;i<=n;i++)
    {
        L[i]=sum(n)-sum(a[i]);
        cc(a[i],1);
    }
    for (i=1;i<=n;i++)
    c[i]=0;
    for (i=n;i>=1;i--)
    {
        R[i]=sum(a[i]);
        cc(a[i],1);
    }
    for (i=1;i<=n;i++)
    c[i]=0;
    for (i=1;i<=n;i++)
        Ans=Ans+L[i];
    for (i=1;i<=m;i++)
        scanf("%d",&b[i]);
    solve(1,m);
    for (i=1;i<=m;i++)
    {
        printf("%lld\n",Ans);
        Ans=Ans-L[id[b[i]]]-R[id[b[i]]]+ans[i];
    }    
}