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Queue Stack Reverse Polish Notation - Practice Exercises Java


Lesson 11:

Dynamic memory management


Exercise 11.4:

Queue Stack Reverse Polish Notation


Objetive:

Create a program that reads from a text file one expression in Reverse Polish Notation like, for example:

3 4 6 5 - + * 6 +
(Result 21)

Each item will be stored in a queue.

Once the queue has all the items stored, you will have to store them from the queue to a stack (using class Queue and Stack provided in Java).

Finally, you will operate with the stack in order to get the correct result of the expression in RPN, and you will show it by console.


Source Code:


package FileTextQueue;
import java.util.*;
public class Main
{
	public static void main(String[] args)
	{
		System.out.print("Introduce el nombre del archivo: ");
		String nombreFichero = new Scanner(System.in).nextLine();

		if (!(new java.io.File(nombreFichero)).isFile())
		{
			System.out.print("El archivo no existe");
			return;
		}

		try
		{
			boolean depurando = true;

			java.io.FileReader ficheroTexto;
		    java.io.BufferedReader ficheroTextoBufferedReader = 
            new java.io.BufferedReader(ficheroTexto);

			ficheroTexto = new java.io.FileReader(nombreFichero);
			String line = " ";

			LinkedList micola = new LinkedList();

			do
			{
				line = ficheroTextoBufferedReader.readLine();
				if (line != null)
				{
					micola.offer(line);
				}
			} while (line != null);

			ficheroTexto.close();

			Stack miPila = new Stack();

			int numero1 = 0, numero2 = 0;

			int cantidadCola = micola.size();

			String valorCola;
			String[] valores_linea;

			for (int i = 0; i < cantidadCola; i++)
			{
				valorCola = (String)micola.poll();
				valores_linea = valorCola.split("[ ]", -1);

				for (int c = 0; c < valores_linea.length; c++)
				{
					switch (valores_linea[c])
					{
						case "+":
							numero1 = (int)miPila.pop();
							numero2 = (int)miPila.pop();

							miPila.push(numero2 + numero1);

							break;
						case "-":
							numero1 = (int)miPila.pop();
							numero2 = (int)miPila.pop();

							miPila.push(numero2 - numero1);
							break;
						case "*":
							numero1 = (int)miPila.pop();
							numero2 = (int)miPila.pop();

							miPila.push(numero2 * numero1);
							break;
						case "/":
							numero1 = (int)miPila.pop();
							numero2 = (int)miPila.pop();

							miPila.push(numero2 / numero1);
							break;
						default:
							// Almacenamos valores enteros
							miPila.push(valores_linea[c]);
							break;
					}
				}

				for (int j = 0; j < miPila.size(); j++)
				{
					System.out.println(miPila.pop());
				}
			}

			if (depurando)
			{
				new Scanner(System.in).nextLine();
			}
		}

		catch (RuntimeException e)
		{
			System.out.println("Error, " + e.getMessage());
		}
	}
}
Exercisey 11.4

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