/* * Stack interface. * Stack works on LIFO (Last-in-first-out) basis. * Each node is added to and removed from the top of the stack. * This interface states mandatory methods which each stack must implement. * Author - Aakash "Ash" Jain. * Contact - [email protected] */ package Stacks; public abstract interface Stack { // Add object to the top of the stack, // return 0; 1 in case of an exception. public int push(Object val); // O(1) // Return topmost node on the stack, // null in stack in empty, -1 in case of an exception. public Object peek(); // O(1) // Remove and return topmost node on the stack, // return null if stack is empty, -1 in case of an exception. public Object pop(); // O(1) // Remove node at specified index and return 0, 1 in case of invalid index, // -1 in case of an exception. Does NOT support negative or overflowing indexes. public int remove(int index); // O(n) // Clear the stack and return 0, 1 if some error occurs. public int clear(); // O(1) for simple stack using arrays, O(n) for linked stack. // Return true if the stack is empty, false otherwise. public boolean isEmpty(); // O(1) // Return the length of the stack. (Total number of nodes) public int getLength(); // Stringify the stack data. @Override public String toString(); // O(n) }