/* ==========================================================
   This demo program uses Java's generic Stack class
   ========================================================== */
import java.util.Stack;
import java.util.Arrays;

public class RPN
{
    public static int evalRPN(String[] inp)
    {
	Stack<Integer> opStack = new Stack<>();
	String s;

	for ( int i = 0; i < inp.length; i++ )
	{
	    s = inp[i];			   // Next item in input (as String !)
	    System.out.println(">" + s);

	    if ( s.equals("x") || s.equals("/") ||
		 s.equals("+") || s.equals("-")     )
	    {
                // Symbol is an operator

		int o2 = opStack.pop();     // Get the last 2 operands
		int o1 = opStack.pop();

		int r = operate(s, o1, o2); // Perform operation
	        opStack.push( r );	    // Save result on stack
	    }
	    else
                // Symbol is an number (i.e.: operand)
                opStack.push( Integer.parseInt(s) ); // Save it as Integer

            System.out.println("opStack = " + opStack);
	}

	return opStack.pop(); // Return result (was saved on stack)
    }

    public static int operate( String op, int o1, int o2 )
    {

        if ( op.equals("x") )
        {
            System.out.println(">>>" + o1 + " * " + o2);
	    return( o1*o2 );
        }
        else if ( op.equals("/") )
        {
            System.out.println(">>>" + o1 + " / " + o2);
	    return( o1/o2 );
        }
	else if ( op.equals("+") )
	{
            System.out.println(">>>" + o1 + " + " + o2);
            return( o1+o2 );
	}
	else if ( op.equals("-") )
	{
	    System.out.println(">>>" + o1 + " - " + o2);
            return( o1-o2 );
	}
	else
	    return 0;
    }
}