RT，退化到不会做黄题了。

思路：Splay 维护 pre 和 next，map 维护出现与否。

#include<bits/stdc++.h>
using namespace std;
int val[100005] , n , x;
char op;
struct Splay
{
	int rt , tot , fa[100005] , ch[100005][5] , sz[100005] , cnt[100005];
	inline void maintain(const int &x)
	{
		sz[x] = sz[ch[x][0]] + sz[ch[x][1]] + cnt[x];
		return;
	}
	inline bool get(const int &x)
	{
		return x == ch[fa[x]][1];
	}
	inline void clear(const int &x)
	{
		ch[x][0] = ch[x][1] = fa[x] = val[x] = sz[x] = cnt[x] = 0;
		return;
	}
	inline void rotate(const int &x)
	{
		const int y = fa[x] , z = fa[y] , chk = get(x);
		if(chk ^ 1)
		{
			ch[y][chk] = ch[x][1];
			if(ch[x][1])
			{
				fa[ch[x][1]] = y;
			}
			ch[x][1] = y;
		}
		else
		{
			ch[y][chk] = ch[x][0];
			if(ch[x][0])
			{
				fa[ch[x][0]] = y;
			}
			ch[x][0] = y;
		}
		fa[y] = x;
		fa[x] = z;
		if(z)
		{
			if(y == ch[z][1])
			{
				ch[z][1] = x;
			}
			else
			{
				ch[z][0] = x;
			}
		}
		maintain(y);
		maintain(x);
		return;
	}
	inline void splay(const int &x)
	{
		for(register int f = fa[x] ; f = fa[x] , f ; rotate(x))
		{
			if(fa[f])
			{
				if(get(x) == get(f))
				{
					rotate(f);
				}
				else
				{
					rotate(x);
				}
			}
		}
		rt = x;
		return;
	}	
	inline void ins(const int &k)
	{
		if(!rt)
		{
			tot++;
			val[tot] = k;
			cnt[tot]++;
			rt = tot;
			maintain(rt);
			return;
		}
		register int cur = rt , f = 0;
		while(1)
		{
			if(val[cur] == k)
			{
				cnt[cur]++;
				maintain(cur);
				maintain(f);
				splay(cur);
				return;
			}
			f = cur;
			if(val[cur] < k)
			{
				cur = ch[cur][1];
			}
			else
			{
				cur = ch[cur][0];
			}
			if(!cur)
			{
				tot++;
				val[tot] = k;
				cnt[tot]++;
				fa[tot] = f;
				if(val[f] < k)
				{
					ch[f][1] = tot;
				}
				else
				{
					ch[f][0] = tot;
				}
				maintain(tot);
				maintain(f);
				splay(tot);
				return;
			}
		}
		return;
	}
	inline int rk(const int &k)
	{
		register int res = 0 , cur = rt;
		while(1)
		{
			if(k < val[cur])
			{
				cur = ch[cur][0];
			}
			else
			{
				res += sz[ch[cur][0]];
				if(!cur)
				{
					return res + 1;
				}
				if(k == val[cur])
				{
					splay(cur);
					return res + 1;
				}
				res += cnt[cur];
				cur = ch[cur][1];
			}
		}
		return 0;
	}
	inline int kth(register int k)
	{
		register int cur = rt;
		while(1)
		{
			if(ch[cur][0] && k <= sz[ch[cur][0]])
			{
				cur = ch[cur][0];
			}
			else
			{
				k -= cnt[cur] + sz[ch[cur][0]];
				if(k <= 0)
				{
					splay(cur);
					return val[cur];
				}
				cur = ch[cur][1];
			}
		}
		return 0;
	}
	inline int pre()
	{
		register int cur = ch[rt][0];
		if(!cur)
		{
			return cur;
		}
		while(ch[cur][1])
		{
			cur = ch[cur][1];
		}
		splay(cur);
		return cur;
	}
	inline int nxt()
	{
		register int cur = ch[rt][1];
		if(!cur)
		{
			return cur;
		}
		while(ch[cur][0])
		{
			cur = ch[cur][0];
		}
		splay(cur);
		return cur;
	}
	inline void del(const int k)
	{
		rk(k);
    	if(cnt[rt] > 1)
		{
			cnt[rt]--;
			maintain(rt);
			return;
		}
		if(!ch[rt][0] && !ch[rt][1])
		{
			clear(rt);
			rt = 0;
			return;
		}
		if(!ch[rt][0])
		{
			int cur = rt;
			rt = ch[rt][1];
			fa[rt] = 0;
			clear(cur);
			return;
		}
		if(!ch[rt][1])
		{
			int cur = rt;
			rt = ch[rt][0];
			fa[rt] = 0;
			clear(cur);
			return;
		}
		int cur = rt , x = pre();
		fa[ch[cur][1]] = x;
		ch[x][1] = ch[cur][1];
		clear(cur);
		maintain(rt);
		return;
	}
}tree;
int l , r , tsz;
map<int , bool> mp;
int main()
{
	ios::sync_with_stdio(0);
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin >> n;
	while(n--)
	{
		cin >> op >> x;
		if(op == '1')
		{
			if(mp[x] == 1)
			{
				continue;
			}
			tree.ins(x);
			mp[x] = 1;
			tsz++;
		}
		else
		{
			if(!tsz)
			{
				cout << "Empty\n";
				continue; 
			}
			if(mp[x])
			{
				cout << x <<'\n';
				mp[x] = 0;
				tree.del(x);
				tsz--;
				continue;
			}
			l = val[tree.pre()];
			r = val[tree.nxt()];
			if(x - l <= r - x)
			{
				mp[l] = 0;
				tree.del(l);
				cout << l << '\n';
				tsz--; 
			}
			else
			{
				mp[r] = 0;
				tree.del(r);
				cout << r << '\n';
				tsz--;
			}
		}
	}
	return 0;
}

我不希望看到：随便贴一份 AC 代码而不说明我这份代码错在哪里的情况。

球各位大佬帮忙！