830. Positions of Large Groups

Easy

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".

A group is identified by an interval [start, end], where start and end denote the start and end indices (inclusive) of the group. In the above example, "xxxx" has the interval [3,6].

A group is considered large if it has 3 or more characters.

Return the intervals of every large group sorted in increasing order by start index.

Solution

class Solution:
    def largeGroupPositions(self, s: str) -> List[List[int]]:
        n = len(s)
        i = 0
        res = []

        while i < n:
            j = 1
            while i + j < n and s[i] == s[i + j]:
                j += 1
            if j > 2:
                res.append([i, i + j - 1])
            i += j

        return res