Evaluate Reverse Polish Notationpo

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

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Easy one

public class Solution {
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack = new Stack<Integer>();
        int result = 0;
        for (String s : tokens) {
            if (s.equals("+")) {
            	result = stack.pop() + stack.pop();
            	stack.push(result);
            } else if (s.equals("-")) {
            	result = -stack.pop() + stack.pop();
            	stack.push(result);
            } else if (s.equals("*")) {
            	result = stack.pop() * stack.pop();
            	stack.push(result);
            } else if (s.equals("/")) {
            	int a = stack.pop(); result = stack.pop()/a;
            	stack.push(result);
            } else {
                stack.push(Integer.parseInt(s));
            }
        }
        return stack.pop();
    }
}