题目

问题：能正常输出empty，但是第二个样例会无限输出s

#include<iostream>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
string str;
vector<int> alt , del;
const int N = 1000010;
int l[N] , r[N];
bool vis[N];
bool f[N];
void insert(int k){
	if(!vis[k]){
		vis[k] = true;
		del.push_back(k);
	}
}
int main(){
	cin >> str;
	int n = str.size();
	str = ' ' + str;
	for(int i = 1;i <= n;i++){
		l[i] = i - 1 , r[i] = i + 1;
		alt.push_back(i);
	} 
	r[0] = 1 , l[n + 1] = n;
	str[0] = str[n + 1] = '?';
	for(;;){
		for(int k : alt){
			int a = l[k] , b = k , c = r[k];
			if(a && str[a] != '?' && str[b] == str[a] && str[b] != str[c]){
				insert(b);
				insert(c);
			}
			if(c != n + 1 && str[c] != '?' && str[b] != str[a] && str[b] == str[c]){
				insert(a);
				insert(b);
			}
		}
		if(del.empty()) break;
		alt.clear();
		for(int k : del){
			int a = l[k] , b = k , c = r[k];
			if(a && str[a] != '?' && !vis[a] && !f[a]){
				alt.push_back(a);
				f[a] = true;
			} 
			if(c != n + 1 && str[c] != '?' && !vis[c] && !f[c]){
				alt.push_back(c);
				f[c] = true;
			}
			r[a] = c , l[c] = a;
		}
		del.clear();
		for(int i = r[0];str[i] != '?';i = r[i]) cout << str[i];system("pause");
	}
	if(r[0] == n + 1) puts("EMPTY");
	else for(int i = r[0];str[i] != '?';i = r[i]) cout << str[i];
	return 0;
}