STL模拟

#include<bits/stdc++.h>
using namespace std;
set<int>pre,now;
int main()
{
	int n,q;scanf("%d%d",&n,&q);
	for(int i=1;i<=n;i++)pre.insert(i); 
	while(q--)
	{
		int op,x;scanf("%d",&op);
		if(op==1)
		{
			now.insert(*pre.begin());
			pre.erase(pre.begin());
		}
		else if(op==2)
		{
			scanf("\%d",&x);
			now.erase(x);
		}
		else printf("%d\n",*now.begin());
	}
	return 0;
}