洛谷 P2286 [HNOI2004]宠物收养场

题目传送门

做法：维护一棵Splay，如果现在来的是人，且还有宠物，那就找前驱和后缀与之差值的较小值，否则就加到树上。如果是宠物则同理。（这里的前驱后缀可以等于对应的值）

---

Code:

#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
//Mystery_Sky
//
#define M 1000100
#define INF 0x3f3f3f3f
#define Mod 1000000
inline 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*10+c-'0';c=getchar();}
	return x*f;
}

struct Splay{
	int cnt, size;
	int val;
	int fa, son[2];
}t[M];
int root, tot;
int n, opt, x;
int peo, ani, ans;

inline void push_up(int x) 
{
	if(x) {
		t[x].size = t[x].cnt;
		if(t[x].son[0]) t[x].size += t[t[x].son[0]].size;
		if(t[x].son[1]) t[x].size += t[t[x].son[1]].size;
	}
}
inline bool check(int x) {return t[t[x].fa].son[1] == x;}
inline void Clear(int x) {t[x].val = t[x].size = t[x].cnt = t[x].fa = t[x].son[0] = t[x].son[1] = 0;}
inline int New(int x, int fa) 
{
	t[++tot].val = x;
	t[tot].size = t[tot].cnt = 1;
	t[tot].son[0] = t[tot].son[1] = 0;
	t[tot].fa = fa;
	return tot;
}

inline void Rotate(int x)
{
	int y = t[x].fa, z = t[y].fa, k = check(x), w = t[x].son[k^1];
	t[y].son[k] = w; t[t[y].son[k]].fa = y;
	t[y].fa = x;
	t[x].son[k^1] = y;
	t[x].fa = z;
	if(z) t[z].son[t[z].son[1] == y] = x;
	push_up(y);
	push_up(x);
}

inline void splay(int x)//Splay->一直Rotate到根节点 
{
	for(int y; (y = t[x].fa); Rotate(x))
		if(t[y].fa) Rotate((check(x) == check(y) ? y : x));
	root = x;
}

inline void Insert(int x)
{
	if(!root) {
		root = New(x, 0);
		return;
	}
	int now = root, y = 0;
	while(1) {
		//printf("1\n");
		if(t[now].val == x) {
			t[now].cnt++;
			push_up(now), push_up(y);
			splay(now);
			break;
		}
		y = now;
		now = t[now].son[t[now].val < x];
		if(!now) {
			New(x, y);
			t[y].son[t[y].val < x] = tot;
			push_up(y);
			splay(tot);
			return;
		}
	}
}

inline int query_rank(int x)
{
	int ans = 0, now = root;
	while(1) {
		if(x < t[now].val) now = t[now].son[0];
		else {
			ans += t[t[now].son[0]].size;
			if(x == t[now].val) {
				splay(now);
				return ans + 1;	
			}
			ans += t[now].cnt;
			now = t[now].son[1];
		}
	}
}

inline int query_val(int rank)
{
	int now = root;
	while(1) {
		if(t[now].son[0] && rank <= t[t[now].son[0]].size) now = t[now].son[0];
		else {
			int temp = t[t[now].son[0]].size + t[now].cnt;
			if(rank <= temp) return t[now].val;
			rank -= temp;
			now = t[now].son[1];
		} 
	}
} 

inline int Pre()
{
	int now = t[root].son[0];
	while(t[now].son[1]) now = t[now].son[1];
	return now; 
}

inline int Succ()
{
	int now = t[root].son[1];
	while(t[now].son[0]) now = t[now].son[0];
	return now;
}

inline void Delete(int x)
{
	int q = query_rank(x);
	if(t[root].cnt > 1) {
		t[root].cnt--;
		push_up(root);
		return;
	}
	if(!t[root].son[0] && !t[root].son[1]) {
		Clear(root);
		root = 0;
		return;
	}
	if(!t[root].son[0]) {
		int y = root;
		root = t[y].son[1];
		t[root].fa = 0;
		Clear(y);
		return;
	}
	else if(!t[root].son[1]) {
		int y = root;
		root = t[y].son[0];
		t[root].fa = 0;
		Clear(y);
		return;
	}
	int lc = Pre(), y = root;
	splay(lc);
	t[t[y].son[1]].fa = root;
	t[root].son[1] = t[y].son[1];
	Clear(y);
	push_up(root);
	return;
}

int main() {
	n = read();
	Insert(INF), Insert(-INF);
	for(int i = 1; i <= n; i++) {
		opt = read(), x = read();
		if(opt == 0) {
			if(peo > 0) {
				Insert(x);
				if(t[root].cnt > 1) {
					Delete(x);
				}
				else {
					int pre = Pre();
					int nxt = Succ();
					int del_1 = abs(x - t[pre].val);
					int del_2 = abs(t[nxt].val - x);
					if(del_1 <= del_2) {
						Delete(t[pre].val);
						ans += del_1;
						ans %= Mod;
					}
					else {
						Delete(t[nxt].val);
						ans += del_2;
						ans %= Mod;
					} 
				}
				Delete(x);
				peo--;
			}
			else Insert(x), ani++;
		}
		else {
			if(ani > 0) {
				Insert(x);
				if(t[root].cnt > 1) {
					Delete(x);
				}
				else {
					int pre = Pre();
					int nxt = Succ();
					int del_1 = abs(x - t[pre].val);
					int del_2 = abs(t[nxt].val - x);
					if(del_1 <= del_2) {
						Delete(t[pre].val);
						ans += del_1;
						ans %= Mod;
					}
					else {
						Delete(t[nxt].val);
						ans += del_2;
						ans %= Mod;
					} 
				}
				Delete(x);
				ani--;
			}
			else Insert(x), peo++;
		}
	}
	printf("%d\n", ans);
	return 0;
}