在堆栈的自定义实现中重载==运算符

Question

I'm trying to implement a custom stack that always returns the min element. Effectively thus I'm maintaining two stacks. I've implemented the push method in my custom stack but feel at a bit of a loss implementing the pop. Ideally I'm trying to write a custom overload of for the == operator two compare two nodes. This is my node implementation.

template<typename T> class stack;
template<typename T> class node{
friend class stack<T>;
public:
    node():T(NULL),next(NULL){}
    node(T data):data(data), next(NULL){}
private:
    T data;
    node<T>* next;

};

And here's my stack push and pop

void push(T item){
        node<T>* N = new node<T>(item);

        if(top == nullptr){
            top = N;
            min_top = N;
            ++elements;
            return;
        }
        if(item < min_top->data) N->next = min_top;
        min_top = N;
        N->next = top;
        top = N;
        ++elements;
    }

........... ...........

T pop(){
        if(top == nullptr)throw std::runtime_error("stack empty");

        T item = top->data;
        node<T>* P = top;
        top = P->next;
        delete P;
        --elements;
        return item;

    }

This is the method signature I've defined for the equality overload.

bool operator==(const node<T>& other){

    }

The idea is to pop the minimum element(top of the min stack) of the min_stack if it's the same as the top of the main stack.

Answer 1

If you already have operator< (which you need for a sorted collection of any type), then there's a pattern for correctly defining operator== :

bool operator==(const node<T>& other) const
{
    if (*this < other) return false;
    if (other < *this) return false;
    return true;
}

Or you can make it even more general using std::less :

bool operator==(const node<T>& other) const
{
    using std::less;
    if (less(*this, other)) return false;
    if (less(other, *this)) return false;
    return true;
}