StackUsingArray.java

package com.ds.rani.design;

    /**
     * Implement stack using Array
     */
    class Stack {
        int stackSize;
        int top;
        int a[];

        /**
         * Constructor
         */
        Stack(int size) {
            stackSize = size;
            top = -1;
            a = new int[stackSize];
        }

        /**
         * check whether stack is empty or not
         *
         * @return true if stack is empty and false if not.
         */
        //Time Complexity:o(1)
        // Space complexity:o(1)
        boolean isEmpty() {
            //if top is at -1 it means stack is empty
            return top == -1;
        }


        /**
         * Push the value x into stack and returns boolean value
         *
         * @param x : int value
         * @return returns true if stack has a space and inserts value in a stack else returns false
         */
        //Time Complexity:o(1)
        // Space complexity:o(1)
        boolean push(int x) {
            //There is a space available in the stack for new element
            if (top + 1 < stackSize) {
                top++;
                a[top] = x;
                return true;
            } else {
                //element is not pushed because of stack overflow
                System.out.println( " Stack OverFlow" );
                return false;
            }
        }

        /**
         * pop or remove the elemnt from the stack. If stack doesnt have ny elemnt then print Stack
         * underflow and return 0. else remove the top value return it
         *
         * @return
         */
        //Time Complexity:o(1)
        // Space complexity:o(1)
        int pop() {
            //If stack is empty
            if (isEmpty()) {
                System.out.println( " Stack Underflow" );
                return 0;
            } else {
                return a[top--];
            }
        }

        /**
         * Return the top value of the stack.If stack is empty return 0 else return top element
         *
         * @return int value
         */
        //Time Complexity:o(1)
        // Space complexity:o(1)
        int peek() {
            if (isEmpty()) {
                return 0;
            } else {
                return a[top];
            }
        }
    }
    public class StackUsingArray {
        public static void main(String args[])
        {
            Stack s = new Stack(100);
            System.out.println("Peek():"+s.peek());
            System.out.println("pop():"+s.pop());
            System.out.println("Stack Empty:"+s.isEmpty());
            s.push(10);
            s.push(20);
            s.push(30);
            System.out.println(s.pop() + " Popped from stack");
            System.out.println("Stack Empty:"+s.isEmpty());
            System.out.println(s.pop() + " Popped from stack");
            System.out.println(s.pop() + " Popped from stack");
            System.out.println("Stack Empty:"+s.isEmpty());
        }
    }