bzoj2212: [Poi2011]Tree Rotations

线段树合并，又学了一个破玩意儿，推荐黄嘉泰大神的PPT

实际操作跟主席树差不了多少吧（或者说弱化版主席树？？）

#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long LL;

int n,z,a[8100000],lc[8100000],rc[8100000];
int initytree()
{
    int now=++z;
    scanf("%d",&a[now]);
    if(a[now]==0)
    {
        lc[now]=initytree();
        rc[now]=initytree();
    }
    return now;
}

struct trnode
{
    int lc,rc,c;
}tr[8100000];int trlen,rt[8100000];
int maketree(int x,int l,int r,int p)
{
    if(x==0)x=++trlen;
    if(l==r){tr[x].c=1;return x;}
    
    int mid=(l+r)/2;
    if(p<=mid)tr[x].lc=maketree(tr[x].lc,l,mid,p);
    else       tr[x].rc=maketree(tr[x].rc,mid+1,r,p);
    tr[x].c=tr[tr[x].lc].c+tr[tr[x].rc].c;
    return x;
}
LL ans,ans1,ans2;
int merge(int x,int y)
{
    if(x==0||y==0)return x+y;
    ans1+=(LL(tr[tr[x].lc].c))*(LL(tr[tr[y].rc].c));
    ans2+=(LL(tr[tr[x].rc].c))*(LL(tr[tr[y].lc].c));
    
    tr[x].c+=tr[y].c;
    tr[x].lc=merge(tr[x].lc,tr[y].lc);
    tr[x].rc=merge(tr[x].rc,tr[y].rc);
    return x;
}
void solve(int x)
{
    if(a[x]!=0)return ;
    solve(lc[x]);solve(rc[x]);
    ans1=0;ans2=0;
    rt[x]=merge(rt[lc[x]],rt[rc[x]]);
    ans+=min(ans1,ans2);
}
int main()
{
    scanf("%d",&n);
    z=0;int root=initytree();
    for(int i=1;i<=z;i++)
        if(a[i]!=0)rt[i]=maketree(rt[i],1,n,a[i]);
    ans=0;
    solve(root);
    printf("%lld\n",ans);
    return 0;
}