package 資料結構;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

public class NiBoLanExpression {
    public static void main(String[] args) {
        String expression = "3 4 + 5 × 6 -";
        String[] split = expression.split(" ");
        List<String> list = new ArrayList<String>();
        for (String ele : split) {
            list.add(ele);
        }

        System.out.println(Calculator(list));
    }

    public static int Calculator(List<String> list){
        Stack<String> stack = new Stack<>();
        for(String ele: list){
            if (ele.matches("\\d+")){
                stack.push(ele);
            }else{
                int num2 = Integer.parseInt(stack.pop());
                int num1 = Integer.parseInt(stack.pop());
                int res = 0;

                if (ele.equals("+")){
                    res = num1 + num2;
                }else if (ele.equals("-")){
                    res = num1 - num2;
                }else if (ele.equals("×")){
                    res =  num1 * num2;
                }else if (ele.equals("÷")){
                    res = num1 / num2;
                }else throw new RuntimeException("運算子有誤");
                stack.push(res + "");
            }
        }
        return Integer.parseInt(stack.pop());
    }
}