'''
In a string S of lowercase letters, these letters form consecutive groups of the same character.
For example, a string like S = "abbxxxxzyy" has the groups "a", "bb", "xxxx", "z" and "yy".
Call a group large if it has 3 or more characters. We would like the starting and ending positions of every large group.
The final answer should be in lexicographic order.
Example 1:
Input: "abbxxxxzzy"
Output: [[3,6]]
Explanation: "xxxx" is the single large group with starting 3 and ending positions 6.
Example 2:
Input: "abc"
Output: []
Explanation: We have "a","b" and "c" but no large group.
Example 3:
Input: "abcdddeeeeaabbbcd"
Output: [[3,5],[6,9],[12,14]]
'''
class Solution(object):
def largeGroupPositions(self, S):
"""
:type S: str
:rtype: List[List[int]]
"""
if not S:
return []
result = []
count = 1
prevChar = S[0]
index_i = 0
for index in range(1,len(S)):
if S[index] == prevChar:
count += 1
else:
if count >= 3:
result.append([index_i, index-1])
count = 1
prevChar = S[index]
index_i = index
if count >= 3:
result.append([index_i, len(S)-1])
return result
