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
        LinkedList<Integer> stack = new LinkedList<>();
        for(int i = 0; i < tokens.length; i++) {
            if(isOprater(tokens[i])){
                int num2 = stack.pop();
                int num1 = stack.pop();
                int result = op(num1, tokens[i].charAt(0), num2);
                stack.push(result);
            }else{
                stack.push(Integer.parseInt(tokens[i]));
            }           
        }
        return stack.pop();
    }
    private boolean isOprater(String s){
        return "+".equals(s) || "-".equals(s) || "*".equals(s) || "/".equals(s);
    }
    private int op(int num1, char oprater, int num2) {
        switch (oprater) {
            case '+':
                return num1 + num2;
            case '-':
                return num1 - num2;
            case '*':
                return num1 * num2;
            case '/':
                return num1 / num2;
            default:
                return 0;
        }
    }
}