题解 | 逆波兰表达式求值

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param tokens string字符串一维数组
     * @return int整型
     */
    public int evalRPN (String[] tokens) {
        // write code here
        Stack<String> stack = new Stack<>();

        for (String token : tokens) {
            if (token.equals("+") || token.equals("-") || token.equals("*") ||
                    token.equals("/")) {
                int b = Integer.valueOf(stack.pop());
                int a = Integer.valueOf(stack.pop());
                int c = 0;
                if (token.equals("+") ) c = a + b;
                if (token.equals("-") ) c = a - b;
                if (token.equals("*") ) c = a * b;
                if (token.equals("/") ) c = a / b;
                stack.push(String.valueOf(c));
            } else {
                stack.push(token);
            }
        }
        if (!stack.isEmpty()) return Integer.valueOf(stack.pop());
        else return 0;
    }
}