这题

WA 了，调了 N 天,即将破防！

#include <bits/stdc++.h>
using namespace std;
bool vis[100001];
int cnt[100001];
queue<int> q;
int main(){
	int n;
	cin >> n;
	for (int i = 1; i <= n; i++){
		char com;
		cin >> com;
		if (com == 'a'){
			int k;
			cin >> k;
			if (!vis[k]){
				q.push(k);
				cnt[k]++;
			}
			vis[k] = !vis[k];
		}
		if (com == 'b'){
			while (!q.empty() && (!vis[q.front()] || cnt[q.front()] > 1)){
				cnt[q.front()]--;
				q.pop();
			}
			if (q.empty())
				cout << -1 << endl;
			else {
				cout << q.front() << endl;
				q.pop();
			}
		}
	}
	return 0;
}