2264 - Largest 3-Same-Digit Number in String\.

Easy

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 in num or a good integer.

Example 1:

Input: num = "6777133339"

Output: "777"

Explanation: There are two distinct good integers: "777" and "333".

"777" is the largest, so we return "777".

Example 2:

Input: num = "2300019"

Output: "000"

Explanation: "000" is the only good integer.

Example 3:

Input: num = "42352338"

Output: ""

Explanation: No substring of length 3 consists of only one unique digit. Therefore, there are no good integers.

Constraints:

• 3 <= num.length <= 1000

• num only consists of digits.