数组的包含

public static boolean check(String s1, String s2) {
    char[] s2_arr = s2.toCharArray();
    Arrays.sort(s2_arr);
    for (int i = 0; i < s1.length(); i++) {
      char a = s1.charAt(i);
      int index = Arrays.binarySearch(s2_arr, a);
      if (index < 0)
        return false;
    }
    return true;
  }