후위식 연산

 

import java.util.Scanner;
import java.util.Stack;


public class Main {
    public int solution(String str) {
        int answer = 0;
        Stack<Integer> stack = new Stack<>();
        //숫자들을 일단 스택에 넣어놔라
        for(char x : str.toCharArray()) {
            //숫자일 때
            if(Character.isDigit(x)) stack.push(x-48);
            //연산자를 만났을 때
            else {
                int rt = stack.pop(); //오른쪽 숫자
                int lt = stack.pop(); //왼쪽 숫자
                if(x=='+') stack.push(lt+rt);
                else if(x=='-') stack.push(lt-rt);
                else if(x=='*') stack.push(lt*rt);
                else if(x=='/') stack.push(lt/rt);
            }
            answer = stack.get(0);

        }

        return answer;
    }

    public static void main(String[] args){
        Main T = new Main();
        Scanner kb = new Scanner(System.in);
        String str = kb.next();

        System.out.print(T.solution(str));
    }
}