【题解】 [HNOI2004]宠物收养场（Splay）

懒得复制，戳我戳我

Solution:

• \(Splay\)板子，注意交换的地方，然后就是注意不要越界node[x]，应该是\(node[now]\)，其次就是数组可以开大点

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Code:

//It is coded by Ning_Mew on 4.10
#include<bits/stdc++.h>
#define ls(x) node[x].ch[0]
#define rs(x) node[x].ch[1]
#define fa(x) node[x].fa
#define root node[0].ch[1]
using namespace std;

const int maxn=200000+10,INF=1e9+7,MOD=1e6;

int n,ans=0,tot=0;
struct Node {
	int fa,ch[2],cnt,val,size;
} node[maxn];

void update(int x) {node[x].size=node[ls(x)].size+node[rs(x)].size+node[x].cnt;}
void connect(int x,int fa,int how) {node[x].fa=fa;node[fa].ch[how]=x;}
int ident(int x) {return x==node[fa(x)].ch[0]?0:1;}
void rorate(int x) {
	int Y=fa(x),R=fa(Y);	int Yson=ident(x),Rson=ident(Y);
	connect(node[x].ch[Yson^1],Y,Yson);
	connect(Y,x,Yson^1);
	connect(x,R,Rson);
	update(Y);update(x);
}
void Splay(int x,int goal) {
	int to=fa(goal);
	while(fa(x)!=to) {
		if(fa(fa(x))==to)rorate(x);
		else if(ident(x)==ident(fa(x)))rorate(fa(x)),rorate(x);
		else rorate(x),rorate(x);
	}
}
int newnode(int x,int fa) {node[++tot].val=x;node[tot].cnt=node[tot].size=1;node[tot].fa=fa;return tot;}
void ins(int x) {
	int now=root;
	if(!root) {newnode(x,0);root=tot;return;
	} else {
		while(1) {
			node[now].size++;
			if(node[now].val==x) {node[now].cnt++;Splay(now,root);return;}
			int nxt=x<node[now].val?0:1;
			if(!node[now].ch[nxt]) {
				int p=newnode(x,now);
				node[now].ch[nxt]=p; Splay(p,root);
				return;
			}
			now=node[now].ch[nxt];
		}
	}
}
int find(int x) {
	int now=root;
	while(1) {
		if(!now)return 0;
		if(node[now].val==x) {Splay(now,root);return now;}
		int nxt=x<node[now].val?0:1;
		now=node[now].ch[nxt];
	}
}
void del(int x) {
	int pos=find(x);
	if(!pos)return;
	if(node[pos].cnt>1) {node[pos].cnt--;node[pos].size--;return;}
	if(!node[pos].ch[0]&&!node[pos].ch[1]) {root=0;return;}
	if(!node[pos].ch[0]) {root=node[pos].ch[1];node[root].fa=0;return;
	} else {
		int left=ls(pos);///
		while(rs(left))left=rs(left);
		Splay(left,node[pos].ch[0]);
		connect(node[pos].ch[1],left,1);
		connect(left,0,1);
		update(left);return;
	}
}
int lower(int x) {
	int now=root,ans=-INF;
	while(now) {
		if(node[now].val<=x)ans=max(ans,node[now].val);
		int nxt=x<=node[now].val?0:1;
		now=node[now].ch[nxt];
	}
	return ans;
}
int upper(int x) {
	int now=root,ans=INF;
	while(now) {
		if(node[now].val>=x)ans=min(ans,node[now].val);
		int nxt=x<node[now].val?0:1;
		now=node[now].ch[nxt];
	}
	return ans;
}
int num[5];
int main() {
	scanf("%d",&n);
	int x,opt,stat=0;
	for(int i=1; i<=n; i++) {
		scanf("%d%d",&opt,&x);
		if(num[stat]==0) {
			ins(x);
			num[opt]++;
			stat=opt;/*cout<<"ins finished"<<endl;*/
		} else {
			if(opt==stat)ins(x),num[opt]++/*,cout<<"ins finished"<<endl*/;
			else {
				num[stat]--;
				int up=upper(x),low=lower(x),box=INF;
				if(up!=INF)box=min(box,abs(x-up));
				if(low!=-INF)box=min(box,abs(x-low));
				//cout<<up<<' '<<low<<' '<<box<<endl;
				ans=(ans+box)%MOD;
				if(box==abs(x-low))del(low);
				else del(up);
				//cout<<"del finished"<<endl;
			}
		}
		//cout<<"--"<<stat<<endl;
	}
	printf("%d\n",ans);
	return 0;
}