830. Positions of Large Groups

Python

class Solution(object):
    def largeGroupPositions(self, s):
        """
        :type s: str
        :rtype: List[List[int]]
        """
        result = list()
        before_str = ""
        start_index = -1
        
        for i, alphabet in enumerate(s+ " "):
            if alphabet != before_str: # 현재 값과 이전 값이 다름
                if i - start_index + 1 > 3:
                    result.append([start_index, i - 1])
                    
                before_str = alphabet
                start_index = i
            
        return result