230517 수식 최대화

private long max = 0;
private List<Long> operandList;
private List<String> operatorList;
public long solution(String expression) {
    permutation(expression, 0, 3, new String[] { "+", "-", "*" }, new boolean[3], "");
    return max;
}

private void permutation(String expression, int startDepth, int targetDepth, String[] arr, boolean[] check, String result) {
    if (startDepth == targetDepth) {
        calculate(expression, result);
    } else {
        for (int i = 0; i < arr.length; i++) {
            if (!check[i]) {
                check[i] = true;
                permutation(expression, startDepth + 1, targetDepth, arr, check, result + arr[i]);
                check[i] = false;
            }
        }
    }
}

private void calculate(String expression, String operators) {
    operandList = new LinkedList<>();
    operatorList = new LinkedList<>();

    StringBuilder nextValue = init(expression);

    operandList.add(Long.parseLong(nextValue.toString()));

    for (int i = 0; i < 3; i++) {
        String nowOperator = String.valueOf(operators.charAt(i));

        while (!operatorList.isEmpty()) {
            int index = operatorList.indexOf(nowOperator);

            if (index == -1) {
                break;
            } else {
                switch (nowOperator) {
                    case "+":
                        operandList.add(index, operandList.get(index) + operandList.get(index + 1));
                        break;
                    case "-":
                        operandList.add(index, operandList.get(index) - operandList.get(index + 1));
                        break;
                    case "*":
                        operandList.add(index, operandList.get(index) * operandList.get(index + 1));
                        break;
                    default:
                        break;
                }

                operandList.remove(index + 1);
                operandList.remove(index + 1);

                operatorList.remove(index);
            }
        }
    }

    max = Math.max(max, Math.abs(operandList.get(0)));
}

private StringBuilder init(String expression) {
    StringBuilder result = new StringBuilder();

    for (int i = 0; i < expression.length(); i++) {
        char ch = expression.charAt(i);
        if (ch == '+' || ch == '-' || ch == '*') {
            operandList.add(Long.parseLong(result.toString()));
            result = new StringBuilder();
            operatorList.add(String.valueOf(ch));
        } else {
            result.append(ch);
        }
    }
    return result;
}

출처:https://school.programmers.co.kr/learn/courses/30/lessons/67257