BZOJ2212 Poi2011Tree Rotations（线段树合并）

#include<iostream> 
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
int read()
{
    int x=0,f=1;char c=getchar();
    while (c<‘0‘||c>‘9‘) {if (c==‘-‘) f=-1;c=getchar();}
    while (c>=‘0‘&&c<=‘9‘) x=(x<<1)+(x<<3)+(c^48),c=getchar();
    return x*f;
}
#define N 400010
int n,cnt=0,tot=0,root[N];
long long ans=0,ansl,ansr;
struct data{int l,r,x;}tree[N<<5];
void add(int &k,int l,int r,int x)
{
    if (!k) k=++cnt;
    tree[k].x++;
    if (l==r) return;
    int mid=l+r>>1;
    if (x<=mid) add(tree[k].l,l,mid,x);
    else add(tree[k].r,mid+1,r,x);
}
int merge(int x,int y,int l,int r)
{
    if (!x||!y) return x|y;
    ansl+=1ll*tree[tree[x].l].x*tree[tree[y].r].x;
    ansr+=1ll*tree[tree[x].r].x*tree[tree[y].l].x;
    tree[x].x+=tree[y].x;
    int mid=l+r>>1;
    tree[x].l=merge(tree[x].l,tree[y].l,l,mid),
    tree[x].r=merge(tree[x].r,tree[y].r,mid+1,r);
    return x;
}
int get()
{
    int x=read(),t=++tot;
    if (x) add(root[t],1,n,x);
    else 
    {
        int l=get(),r=get();
        ansl=0,ansr=0;
        root[t]=merge(root[l],root[r],1,n);
        ans+=min(ansl,ansr);
    }
    return t;
}
int main()
{
    freopen("bzoj2212.in","r",stdin);
    freopen("bzoj2212.out","w",stdout);
    n=read();
    get();
    cout<<ans;
    fclose(stdin);fclose(stdout);
    return 0;
}