QueueOnList2017

#include <assert.h>
#include <iostream>
using std::cin;
using std::cout;

struct CListNode {
    int Data;
    CListNode* Next;

    explicit CListNode( int data ) : Data( data ), Next( nullptr ) {}
};

class CQueue {
public:
    CQueue() : head( nullptr ), tail( nullptr ) {}
    CQueue( const CQueue& ) = delete;
    CQueue( CQueue&& ) = delete;
    ~CQueue();
    CQueue& operator=( const CQueue& ) = delete;

    // Добавление в очередь.
    void Enqueue( int data );
    // Извлечение. Если очередь пуста, то возвращает -1.
    int Dequeue();
    bool IsEmpty() const { return head == nullptr; }

private:
    CListNode* head;
    CListNode* tail;
};

CQueue::~CQueue()
{
    while( !IsEmpty() ) {
        Dequeue();
    }
}

void CQueue::Enqueue( int data )
{
    if( head == nullptr ) {
        assert( tail == nullptr );
        head = new CListNode( data );
        tail = head;
    } else {
        tail->Next = new CListNode( data );
        tail = tail->Next;
    }
}

int CQueue::Dequeue()
{
    if( head == nullptr ) {
        return -1;
    }

    // Случай, когда в очереди остался один элемент, обрабатываем отдельно.
    if( head == tail ) {
        const int result = head->Data;
        delete head;
        head = nullptr;
        tail = nullptr;
        return result;
    }

    const int result = head->Data;
    CListNode* toDelete = head;
    head = head->Next;
    delete toDelete;
    return result;
}

int main()
{
    int commandsCount = 0;
    cin >> commandsCount;

    CQueue queue;
    for( int i = 0; i < commandsCount; ++i ) {
        int command = 0;
        int value = 0;
        cin >> command >> value;
        switch( command ) {
        case 3:
            queue.Enqueue( value );
            break;
        case 2:
            if( queue.Dequeue() != value ) {
                cout << "NO";
                return 0;
            }
            break;
        default:
            assert( false );
        }
    }
    cout << "YES";
    return 0;
}