P3521 【[POI2011]ROT-Tree Rotations】

Seeing that the big guys are talking about importing cancer

But because the input is recursive from top to bottom

Merging multiple line segment trees is also recursive (first merge the bottom and then go up)

So ask for the answer when you can enter

Probably

int dfs(){
    
    
	int x;
	scanf("%d",&x);
	if(x!=0) return new_node(x);//叶子节点就直接加一个点
	return merge(dfs(),dfs());//不然就递归合并两个子树
}
int main(){
    
    
	cin>>n;
	cout<<tree[dfs()].ans;
}

Then complete the two functions new_node() and merge().

#include <bits/stdc++.h>
#define N 50000100
#define mid ((l+r)>>1)
using namespace std;
int n,nn;
struct node{
    
    
	int lson,rson,sum;
	long long ans;
}tree[N];
inline int new_node(int x,int l=1,int r=n){
    
    
	int k=++nn;
	tree[nn].sum=1;
	if(l==r) return nn;
	if(x<=mid) tree[nn].lson=new_node(x,l,mid);
	else tree[nn].rson=new_node(x,mid+1,r);
	return k;
}
long long res0,res1;
inline int merge(int x,int y,int l=1,int r=n){
    
    
	if(!y||!x){
    
     res0=res1=0; return x|y; }
	tree[x].ans=tree[x].ans+tree[y].ans;
	long long aa=1ll*tree[tree[x].rson].sum*tree[tree[y].lson].sum,bb=1ll*tree[tree[x].lson].sum*tree[tree[y].rson].sum;
	tree[x].lson=merge(tree[x].lson,tree[y].lson,l,mid);//合并左子树 
	aa+=res0; bb+=res1;
	tree[x].rson=merge(tree[x].rson,tree[y].rson,mid+1,r);//合并右子树 
	aa+=res0; bb+=res1;
	tree[x].ans+=min(aa,bb);
	tree[x].sum=tree[tree[x].lson].sum+tree[tree[x].rson].sum; 
	res0=aa,res1=bb;
	return x;
}
inline int dfs(){
    
    
	int x;
	scanf("%d",&x);
	if(x!=0) return new_node(x);
	return merge(dfs(),dfs());
}
int main(){
    
    
	cin>>n;
	cout<<tree[dfs()].ans;
}

The card space has been stuck for a long time (I'm too bad at writing to the memory pool