CODE 147. Evaluate Reverse Polish Notation

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Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /.
Each operand may be an integer or another expression.
Some examples:

["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

public class Solution {
	public int evalRPN(String[] tokens) {
		// IMPORTANT: Please reset any member data you declared, as
		// the same Solution instance will be reused for each test case.
		Stack<Integer> numbers = new Stack<Integer>();
		for (String token : tokens) {
			if (token.equals("+") || token.equals("-") || token.equals("*")
					|| token.equals("/")) {
				int number2 = numbers.pop();
				int number1 = numbers.pop();
				if (token.equals("+")) {
					numbers.push(number1 + number2);
				}
				if (token.equals("-")) {
					numbers.push(number1 - number2);
				}
				if (token.equals("*")) {
					numbers.push(number1 * number2);
				}
				if (token.equals("/")) {
					numbers.push(number1 / number2);
				}
			} else {
				numbers.push(Integer.valueOf(token));
			}
		}
		return numbers.pop();
	}