2020 카카오 인턴십수식 - 최대화

import java.util.ArrayList;

public class Solution {

    static char[] arr = { '*', '+', '-' };
    static int N = 3;
    static ArrayList<Long> exp = new ArrayList();
    static ArrayList<Character> operations = new ArrayList();
    static long answer = Long.MIN_VALUE;
    public static long solution(String expression) {

        String n = "";
        for(int i=0; i<expression.length(); i++) {
            if(expression.charAt(i) >= '0' && expression.charAt(i) <= '9') {
                n += expression.charAt(i);
            } else {
                exp.add(Long.parseLong(n));
                n = "";
                operations.add(expression.charAt(i));
            }
            if(i == expression.length()-1) exp.add(Long.parseLong(n));
        }

        perm(0);
        return answer;
    }

    public static void perm(int depth) {
        if (depth == N) {
            answer = Math.max(Math.abs(calc(arr)), answer);
            return;
        }
        for (int i = depth; i < N; i++) {
            rightRotate(depth, i);
            perm(depth + 1);
            leftRotate(depth, i);
        }
    }

    public static Long calc(char[] priority) {

        ArrayList<Long> num = new ArrayList(exp);  
        ArrayList<Character> ops = new ArrayList(operations);

        for(int i=0; i<priority.length; i++) {

            for(int j=0; j<ops.size(); j++) {

                if(priority[i] == ops.get(j)) {

                    long result = 0;

                    if(ops.get(j) == '*') {
                        result = num.get(j) * num.get(j+1);
                    } else if(ops.get(j) == '+') {                        
                        result = num.get(j) + num.get(j+1);
                    } else if(ops.get(j) == '-') {
                        result = num.get(j) - num.get(j+1);
                    }
                    num.set(j, result);
                    num.remove(j+1);
                    ops.remove(j);
                    j--;
                }    
            }
        }

        return num.get(0);

    }

    public static void leftRotate(int s, int e) {
        char temp = arr[s];
        for (int i = s; i < e; i++) {
            arr[i] = arr[i + 1];
        }
        arr[e] = temp;
    }

    public static void rightRotate(int s, int e) {
        char temp = arr[e];
        for (int i = e; i > s; i--) {
            arr[i] = arr[i - 1];
        }
        arr[s] = temp;
    }


}