[leetcode] Evaluate Reverse Polish Notation

import java.util.Stack;

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

        return stack.pop();
    }

    public static void main(String[] args) {
        System.out.println(new Solution().evalRPN(new String[] { "2", "1", "+",
                "3", "*" }));
        System.out.println(new Solution().evalRPN(new String[] { "4", "13",
                "5", "/", "+" }));
    }

}