240302 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));
		calculateOperators(nowOperator);
	}

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

private void calculateOperators(String nowOperator) {
	int size = operatorList.size();
	for (int i = 0; i < size; i++) {
		String op = operatorList.get(i);
		if (op.equals(nowOperator)) {
			long operand1 = operandList.remove(i);
			long operand2 = operandList.remove(i);
			long result = 0;
			switch (nowOperator) {
				case "+":
					result = operand1 + operand2;
					break;
				case "-":
					result = operand1 - operand2;
					break;
				case "*":
					result = operand1 * operand2;
					break;
			}
			operandList.add(i, result);
			operatorList.remove(i);
			i--;
			size--;
		}
	}
}

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