231221 파일명 정렬

public String[] solution(String[] files) {
	Arrays.sort(files, (o1, o2) -> {
		String[] part1 = modPart(o1);
		String[] part2 = modPart(o2);

		int headComparing = part1[0].compareTo(part2[0]);
		if (headComparing != 0) {
			return headComparing;
		}

		return Integer.compare(Integer.parseInt(part1[1]), Integer.parseInt(part2[1]));
	});

	return files;
}

private String[] modPart(String s) {
	String[] part = new String[3];
	boolean state = false;
	int numberStartIdx = -1;

	int i = 0;
	for (char currentChar : s.toCharArray()) {
		if (!state && isNumber(currentChar)) {
			part[0] = s.substring(0, i).toLowerCase();
			numberStartIdx = i;
			state = true;
		} else if (state && !isNumber(currentChar)) {
			String number = s.substring(numberStartIdx, i);
			if (number.length() > 5) {
				i -= (number.length() - 5);
			}
			part[1] = s.substring(numberStartIdx, i);
			part[2] = s.substring(i);
			break;
		}
		i++;
	}

	if (part[1] == null) {
		String number = s.substring(numberStartIdx, i);
		if (number.length() > 5) {
			i -= (number.length() - 5);
		}
		part[1] = s.substring(numberStartIdx, i);
		part[2] = s.substring(i);
	}

	return part;
}

private boolean isNumber(char c) {
	return Character.isDigit(c);
}

출처:https://school.programmers.co.kr/learn/courses/30/lessons/17686