/*
 * This class implements a stack by directly using a linked list.
 */
#ifndef _lnkstack_h_
#define _lnkstack_h_

template <typename T>
class Stack {
public:
	// Initialize the stack empty.
	Stack() {
		m_head = nullptr;
		m_size = 0;
	}

	// Push the argument item.
	void push(const T &itm) {
		m_head = new node(itm, m_head);
		++m_size;
	}

	// Pop the argument item, and return true, or return false if the
	// the stack is empty.
	bool pop(T &itm) {
		if(m_head == nullptr) return false;
		itm = m_head->data();
		node *zombie = m_head;
		m_head = m_head->next();
		delete zombie;
		--m_size;
		return true;
	}

	// Convenience to pop and return the top object.  Only works
	// for types where T() is a valid expression.
	T pop() {
		T ret;
		if(pop(ret)) return ret;
		return T();
	}

	// Tell if empty.
	bool empty() {
		return m_head == nullptr;
	}

	int size() {
		return m_size;
	}
	
private:
	// Nodes for the linked list.
	class node {
	public:
		node(const T &d, node *n = nullptr) {
			m_data = d;
			m_next = n;
		}
		const T& data() { return m_data; }
		node *next() { return m_next; }
	private:
		T m_data;
		node *m_next;
	};

	node * m_head;		// Head of the linked list.
	int m_size;		// Size of the stack.
};

#endif