Positions of Large Groups in Python

Suppose there is a string S of lowercase letters, these letters form consecutive groups of the same character. So, when a string like S is like "abbxxxxzyy" has the groups "a", "bb", "xxxx", "z" and "yy". A group will be a large group when it has 3 or more characters. We would like the starting and ending positions of every large group.

So, if the input is like "abcdddeeeeaabbbcd", then the output will be [[3,5],[6,9],[12,14]]

To solve this, we will follow these steps −

• ans := a new list
• csum := 0
• for each a, b in make group of letters with consecutive letters, do
  • grp := the grouped item list
  • if size of grp >= 3, then
    • insert a list with (csum,csum + size of grp - 1) into ans
  • csum := csum + size of grp
• return ans

Let us see the following implementation to get better understanding −

Example

 Live Demo

from itertools import groupby
class Solution:
   def largeGroupPositions(self, S):
      ans = []
      csum = 0
      for a, b in groupby(S):
         grp = list(b)
      if len(grp) >= 3:
         ans.append([csum, csum+len(grp)-1])
         csum+=len(grp)
   return ans
ob = Solution()
print(ob.largeGroupPositions("abcdddeeeeaabbbcd"))

Input

"abcdddeeeeaabbbcd"

Output

[[3, 5], [6, 9], [12, 14]]

Arnab Chakraborty

Updated on: 04-Jul-2020

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