159201/assignment3/as3/main.cpp

#include <iostream>
#include <stdexcept>

namespace ads {

template<typename T>
class Queue
{
    struct Node
    {
        T data_;
        Node* next_;
    };

public:
    using SizeType  =   std::size_t;

    void join(T t)
    {
        do_join(std::move(t));
    }

    void leave()
    {
        do_leave();
    }

    T const& front() const
    {
        return head_->data_;
    }


    SizeType size()const
    {
        return size_;
    }

    bool empty()const
    {
        return head_ or tail_;
    }

private:
    Node* head_{nullptr};
    Node* tail_{nullptr};
    SizeType size_{0};

    void do_join(T && t) noexcept
    {
        if(empty())
            head_ = tail_        = new Node{std::move(t), nullptr};
        else
            tail_ = tail_->next_ = new Node{std::move(t), nullptr};
        ++size_;
    }

    void do_leave()
    {
        if(size_ == 0)
            throw std::runtime_error{"underflow!"};

        if(size_ == 1)
        {
            delete head_;
            head_ = tail_ = nullptr;
        }
        else
        {
            auto tmp = head_;
            head_ = head_->next_;
            delete tmp;
        }
        --size_;
    }
};

}//namespace

int main()
{
    return 0;
}