[LeetCode&Python] Problem 830. Positions of Large Groups

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]]

Note:  1 <= S.length <= 1000

class Solution(object):
def largeGroupPositions(self, S):
"""
:type S: str
:rtype: List[List[int]]
"""
start=end=-1
count=0
ans=[] for i in range(len(S)):
if count>0:
if S[i]!=S[i-1]:
if count>=3:
end=i-1
ans.append([start,end])
start=i
count=1
else:
start=i
count=1
else:
count+=1
else:
count+=1
start=i
if count>=3:
ans.append([start,len(S)-1])
return ans

  

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