2264. Largest 3-Same-Digit Number in String

class Solution:
    def largestGoodInteger(self, num: str) -> str:
        previous = num[0]
        count = 1
        largest = ""

        for e in num[1:]:
            if e == previous:
                count += 1
                if count == 3:
                    largest = max(largest, e)
            else:
                count = 1

            previous = e

        return largest * 3