package DataStructures.Stacks;⏎
⏎
import java.util.NoSuchElementException;⏎
⏎
/**⏎
 * @author Varun Upadhyay (https://github.com/varunu28)⏎
 */⏎
⏎
// An implementation of a Stack using a Linked List⏎
⏎
class StackOfLinkedList {⏎
⏎
    public static void main(String[] args) {⏎
⏎
        LinkedListStack stack = new LinkedListStack();⏎
        stack.push(1);⏎
        stack.push(2);⏎
        stack.push(3);⏎
        stack.push(4);⏎
        stack.push(5);⏎
⏎
        System.out.println(stack);⏎
⏎
        System.out.println("Size of stack currently is: " + stack.getSize());⏎
⏎
        assert stack.pop() == 5;⏎
        assert stack.pop() == 4;⏎
⏎
        System.out.println("Top element of stack currently is: " + stack.peek());⏎
    }⏎
}⏎
⏎
// A node class⏎
⏎
class Node {⏎
    public int data;⏎
    public Node next;⏎
⏎
    public Node(int data) {⏎
        this.data = data;⏎
        this.next = null;⏎
    }⏎
}⏎
⏎
/**⏎
 * A class which implements a stack using a linked list⏎
 * <p>⏎
 * Contains all the stack methods : push, pop, printStack, isEmpty⏎
 **/⏎
⏎
class LinkedListStack {⏎
⏎
    /**⏎
     * Top of stack⏎
     */⏎
    Node head;⏎
⏎
    /**⏎
     * Size of stack⏎
     */⏎
    private int size;⏎
⏎
    /**⏎
     * Init properties⏎
     */⏎
    public LinkedListStack() {⏎
        head = null;⏎
        size = 0;⏎
    }⏎
⏎
    /**⏎
     * Add element at top⏎
     *⏎
     * @param x to be added⏎
     * @return <tt>true</tt> if add successfully⏎
     */⏎
    public boolean push(int x) {⏎
        Node newNode = new Node(x);⏎
        newNode.next = head;⏎
        head = newNode;⏎
        size++;⏎
        return true;⏎
    }⏎
⏎
    /**⏎
     * Pop element at top of stack⏎
     *⏎
     * @return element at top of stack⏎
     * @throws NoSuchElementException if stack is empty⏎
     */⏎
    public int pop() {⏎
        if (size == 0) {⏎
            throw new NoSuchElementException("Empty stack. Nothing to pop");⏎
        }⏎
        Node destroy = head;⏎
        head = head.next;⏎
        int retValue = destroy.data;⏎
        destroy = null; // clear to let GC do it's work⏎
        size--;⏎
        return retValue;⏎
    }⏎
⏎
    /**⏎
     * Peek element at top of stack⏎
     *⏎
     * @return element at top of stack⏎
     * @throws NoSuchElementException if stack is empty⏎
     */⏎
    public int peek() {⏎
        if (size == 0) {⏎
            throw new NoSuchElementException("Empty stack. Nothing to pop");⏎
        }⏎
        return head.data;⏎
    }⏎
⏎
    @Override⏎
    public String toString() {⏎
        Node cur = head;⏎
        StringBuilder builder = new StringBuilder();⏎
        while (cur != null) {⏎
            builder.append(cur.data).append("->");⏎
            cur = cur.next;⏎
        }⏎
        return builder.replace(builder.length() - 2, builder.length(), "").toString();⏎
    }⏎
⏎
    /**⏎
     * Check if stack is empty⏎
     *⏎
     * @return <tt>true</tt> if stack is empty, otherwise <tt>false</tt>⏎
     */⏎
    public boolean isEmpty() {⏎
        return size == 0;⏎
    }⏎
⏎
    /**⏎
     * Return size of stack⏎
     *⏎
     * @return size of stack⏎
     */⏎
    public int getSize() {⏎
        return size;⏎
    }⏎
}⏎