leetcode——830. 较大分组的位置

class Solution(object):
    def largeGroupPositions(self, S):
        """
        :type S: str
        :rtype: List[List[int]]
        """
        i=1
        j=0
        k=[]
        while i<len(S):
            #print(i,j)
            if S[i]==S[i-1]:
                i+=1
                if i==len(S):
                    if i-j>2:
                        k.append([j,i-1])
            else:
                if i-j>2:
                    k.append([j,i-1])
                    j=i
                    i+=1
                else:
                    j=i
                    i+=1
        return k