BZOJ 2212: [Poi2011]Tree Rotations

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N=400002;
inline int read(){
char ch=getchar(); int x=0,f=1;
while(ch<'0'||ch>'9'){if(ch=='-')f=-1; ch=getchar();}
while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+ch-'0'; ch=getchar();}
return x*f;
}
int u,v
,l
,r
,ls[N*10],rs[N*10],s[N*10],rt
,tot;
LL ans,c1,c2;
void rtree(int x){
v[x]=read();
if(!v[x]){
l[x]=++u,rtree(l[x]);
r[x]=++u,rtree(r[x]);
}
}
void bulid(int &x,int l,int r,int c){
if(!x)x=++tot;
if(l==r){s[x]=1; return;}
int mid=(l+r)>>1;
if(c<=mid)bulid(ls[x],l,mid,c);
else bulid(rs[x],mid+1,r,c);
s[x]=s[ls[x]]+s[rs[x]];
}
void merge(int &x,int y){
if(!x){x=y; return;}
if(!y)return;
c1+=(LL)s[rs[x]]*s[ls[y]];
c2+=(LL)s[ls[x]]*s[rs[y]];
merge(ls[x],ls[y]);
merge(rs[x],rs[y]);
s[x]=s[ls[x]]+s[rs[x]];
}
void solve(int x){
if(!x)return;
solve(l[x]),solve(r[x]);
if(!v[x]){
c1=c2=0;
merge(rt[l[x]],rt[r[x]]),rt[x]=rt[l[x]];
ans+=min(c1,c2);
}
}
int main()
{
int n=read(),i; tot=0,u=1;
rtree(1);
for(i=1;i<=u;i++)
if(v[i])bulid(rt[i],1,n,v[i]);
solve(1);
printf("%lld\n",ans);
return 0;
}