2264. Largest 3-Same-Digit Number in String

#Problem

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.

https://leetcode.cn/problems/largest-3-same-digit-number-in-string/

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.

#Test Cases

class Solution:
    def largestGoodInteger(self, num: str) -> str:

import pytest

from solution import Solution


@pytest.mark.parametrize('num, expected', [
    ("6777133339", "777"),
    ("2300019", "000"),
    ("42352338", ""),
])
@pytest.mark.parametrize('sol', [Solution()])
def test_solution(sol, num, expected):
    assert sol.largestGoodInteger(num) == expected

#Thoughts

#Code

class Solution:
    def largestGoodInteger(self, num: str) -> str:
        return max((num[i] for i in range(len(num)-2) if num[i] == num[i+1] == num[i+2]), default='') * 3