230807 숫자 짝꿍

public String solution(String X, String Y) {
	StringBuilder sb = new StringBuilder();

	int[] xArr = new int[10];
	int[] yArr = new int[10];

	for (char x : X.toCharArray()) {
		xArr[x - '0']++;
	}
	for (char y : Y.toCharArray()) {
		yArr[y - '0']++;
	}

	for (int i = 9; i >= 0; i--) {
		while (xArr[i] > 0 && yArr[i] > 0) {
			sb.append(i);
			xArr[i]--;
			yArr[i]--;
		}
	}

	if (sb.length() == 0) {
		return "-1";
	}
	if (sb.charAt(0) == '0') {
		return "0";
	}

	return sb.toString();
}

출처:https://school.programmers.co.kr/learn/courses/30/lessons/131128