150-Evaluate-Reverse-Polish-Notation.java

class Solution {

    public int evalRPN(String[] tokens) {
        Stack<Integer> stack = new Stack<>();
        for (String token : tokens) {
            if (token.equals("+")) {
                stack.add(stack.pop() + stack.pop());
            } else if (token.equals("-")) {
                int a = stack.pop();
                int b = stack.pop();
                stack.add(b - a);
            } else if (token.equals("*")) {
                stack.add(stack.pop() * stack.pop());
            } else if (token.equals("/")) {
                int a = stack.pop();
                int b = stack.pop();
                stack.add(b / a);
            } else {
                stack.add(Integer.parseInt(token));
            }
        }
        return stack.pop();
    }
}