/**
 * The ArrayBasedStack class which is an array based implementation of the Stack class
 *
 * @author Quran Kimbrough
 * @version 1.0
 */
public class ArrayBasedStack {
    private int size;
    private int[] stack;
    private int top;

    /**
     * The default constructor which takes the variable size of type int while initializing stack and top
     *
     * @param size the size of the ArrayBasedStack
     */
    public ArrayBasedStack(int size) {
        this.size = size;
        stack = new int[size];
        top = -1;
    }

    /**
     * A mutator method which displays the stack
     */
    public void display() {

        for (int i = 0; i <= top; i++) {
            System.out.print(stack[i] + " ");
        }
        System.out.println();
    }

    /**
     * An accessor method which determines if the stack is empty
     *
     * @return returns whether the stack is empty
     */
    public boolean isEmpty() {
        return top == -1;
    }

    /**
     * An accessor method which returns the top of the stack;
     *
     * @return the top of the stack
     */
    public int peek() {
        if (!isEmpty()) {
            return stack[top];
        } else {
            System.out.println("error: stack empty");
        }
        return -1;
    }

    /**
     * An accessor method which removes from the top of the stack and then returns the top of the stack
     *
     * @return the top of the stack that has been removed
     */
    public int pop() {
        if (!isEmpty()) {
            int x = stack[top];
            top--;
            return x;
        } else {
            System.out.println("error: stack empty");
        }
        return -1;
    }

    /**
     * A mutator method which pushes a value into the stack
     *
     * @param value the int to be pushed
     */
    public void push(int value) {
        if (top == size - 1) {
            System.out.println("error: stack full");
        } else {
            top++;
            stack[top] = value;
        }
    }
}

import java.util.Scanner;

/**
 * The PostFix class which uses the ArrayBased list from LAB2 updated to contain functions relevant to the Stack class.
 *
 * @author QuranKimbrough
 * @version 1.0
 */
public class PostFix {

    /**
     * An accessor method which returns the evaluated PostFix
     *
     * @param input the String to be evaluated for PostFix
     * @return returns the top of the stack
     */
    public static int evaluatePostFix(String input) {
        String[] inputArray = input.split("\\s+");
        int operatorCount = 0, operandCount = 0;
        for (String s : inputArray){
            if (s.equals("+") || s.equals("-") || s.equals("/") || s.equals("*")){
                operatorCount++;
            }else{
                operandCount++;
            }
        }
        if (operandCount == operatorCount + 1) {
            System.out.println("PostFix input is valid");
        }else{
            System.out.println("invalid PostFix input");
            return -1;
        }
        Scanner sc = new Scanner(input);
        ArrayBasedStack stack = new ArrayBasedStack(input.length());

        while (sc.hasNext()) {
            if (sc.hasNextInt()) {
                stack.push(sc.nextInt());
                continue;
            }
            int z = stack.pop();
            int y = stack.pop();
            char op = sc.next().charAt(0);
            if (op == '+')
                stack.push(y + z);
            else if (op == '-')
                stack.push(y - z);
            else if (op == '*')
                stack.push(y * z);
            else if (op == '/')
                stack.push(y / z);
        }
        sc.close();
        System.out.println(stack.peek());
        return stack.peek();
    }


    /**
     * The main method used to drive the PostFix class.
     *
     * @param args arguments
     */
    public static void main(String[] args) {
        evaluatePostFix("3 2 * 11 -");
    }
}