2264. Largest 3-Same-Digit Number in String

You are given a string num representing a large integer. An integer is good if it meets the following conditions: - It is a substring of num with length 3. - It consists of only one unique digit. Return the maximum good integer as a string or an empty string "" if no such integer exists. Note: - A substring is a contiguous sequence of characters within a string. - There may be leading zeroes