显示正在访问未分配的内存

#include <iostream>
#include <cstring>
#include <queue>

using namespace std;

class Node {
	public:
		Node *next,*pre;
		queue<int>num;
		Node() {
			next=pre=NULL;
			while(!num.empty())
				num.pop();
		}
};

void del(Node *n) {
	n->pre->next=n->next;
	n->next->pre=n->pre;
}

void pushq(Node *a,Node *b) {
	while(!b->num.empty()) {
		a->num.push(b->num.front());
		b->num.pop();
	}
}

int main() {
	int n,t,l=-1,num=0;
	cin >> n;
	Node *head,*tail,*m;
	head = new Node;
	tail=head;
	head->next=NULL;
	for(int i=1;i<=n;i++) {
		cin >> t;
		if(t==l) {
			m->num.push(i);
			continue;
		}
		m=new Node;
		m->num.push(i);
		m->pre=tail;
		m->next=NULL;
		tail->next=m;
		l=t;
		tail=m;
	}
	
	tail->next=NULL;
	m=head->next;
	
	while(head->next->next) {
		m=head->next;
		while(m!=NULL) {
			cout << m->num.front() << ' ';
			m->num.pop();
			if(m->num.empty()) {
				if(m->next!=NULL) {
					cout << m->next->num.front() << ' ';
					pushq(m->pre,m->next);
					del(m->next);
				}
				m=m->next;
				del(m->pre);
			}
			else
				m=m->next;
		}
		cout << endl << 1 << endl;
	}
	return 0;
}