[JAVA] Day_01. +/- 계산기

package calc;
 
import java.util.*;
 
public class Main {
 
    public static void main(String[] args) {
        LinkedList<Integer> numList = new LinkedList<Integer>();
        LinkedList<Character> opList = new LinkedList<Character>();
        
        Scanner sc = new Scanner(System.in);
        
        String s = sc.nextLine();
        
        String num = "";
        
        for(int i = 0; i < s.length(); i++)
        {
            char ch = s.charAt(i);
            
            if(ch == '+')
            {
                numList.add(Integer.parseInt(num));
                opList.add(ch);
                num = "";
                continue;
            }
            else if(ch == '-') 
            {
                numList.add(Integer.parseInt(num));
                opList.add(ch);
                num = "";    
                continue;
            }
            num += ch;
        }
        numList.add(Integer.parseInt(num));
 
        while(!opList.isEmpty()) {
            int prevNum = numList.poll();
            int nextNum = numList.poll();
            char op = opList.poll();
            
            if(op == '+') {
                numList.addFirst(prevNum + nextNum);
            } else if(op == '-') {
                numList.addFirst(prevNum - nextNum);
            }
        }
 
        System.out.println(numList.poll());
    }
 
}