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# Python | Find the longest sequence of letters and numbers

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Examples :

`  Input:  geeks123available  Output:  (’available’, 123)  Input:  98apple658pine  Output:  (’apple’, 658) `

Approach # 1: brute force
This is naive or crude method to find the longest sequence of letters and numbers. We take two string variables of type longest_letter and longest_digit . We start the loop and check the consecutive substrings of letters and numbers. At each iteration, we check if the current alphabetic substring is greater than the longest alphabetic or numeric substring, respectively. If so, we assign the current letter and number substring to the longest letter and digit substring, respectively. Otherwise, do nothing.

 ` # Python3 program to find the longest ` ` # sequential substring of a specific type ` ` import ` ` re `   ` def ` ` longestSubstring (s): `   ` longest_letterSeq ` ` = ` ` ’’ ` ` longest_digitSeq ` ` = ` ` ’’ ` ` i ` ` = ` ` 0 ` < p> ` while ` ` (i "` ` len ` ` (s)): `   ` curr_letterSeq ` ` = ` ` ’’ ` ` curr_digitSeq ` ` = ` ` ’’ `   ` # For literal substring ` ` while ` ` (i "` ` len ` ` (s) ` ` and ` ` s [i] .isalpha ()): ` ` ` ` curr_letterS eq ` ` + ` ` = ` ` s [i] ` ` i ` ` + ` ` = ` ` 1 `   ` # For numeric substring ` ` while ` ` (i "` ` len ` ` (s) ` ` and ` ` s [i] .isdigit ()): ` ` curr_digitSeq ` ` + ` ` = ` ` s [i] ` ` ` ` i ` ` + ` ` = ` ` 1 ` ` `  ` ` ` Handle case if character ` ` # is neither a letter nor digit ` ` if ` ` (i & lt; ` ` len ` ` (s) ` ` and ` ` not ` ` (s [i] .isdigit ()) ` ` ` ` and ` ` not ` ` (s [i] .isalpha ())): ` ` i ` ` + ` ` = ` ` 1 `   ` if ` ` (` ` len ` ` (curr_letterSeq)" ` ` len ` ` (longest_letterSeq)): ` ` longest_letterSeq ` ` = ` ` curr_letterSeq ` ` `  ` if ` ` (` ` len ` ` (curr_digitSeq)" ` ` len ` ` (longest_digitSeq)): ` ` longest_digitSeq ` ` = ` ` curr_digitSeq `   ` return ` ` longest_letterSeq, longest_digitSeq `   ` Driver code ` ` str ` ` = ` ` ’3Geeksfor123geeks3’ ` ` print ` ` (longestSubstring (` ` str ` `)) `

Exit:

` (’Geeksfor’,’ 123’) `

Approach # 2: Using Python regular expressions
Python Regex is another method to solve this problem. Find a sequence of substrings of numbers and letters using a Python regex, and then find the longest substring length, respectively.

 ` # Python3 program to find the longest ` ` # sequential substring of a certain type ` ` import ` ` re `   ` def ` ` longestSubstring (` ` str ` `): ` ` ` ` letter ` ` = ` ` max ` ` (re.findall (r ` `’ D + ’` `, ` ` str ` `), key = len ) `` digit = max (re.findall (r ’d +’ , str ), key = len )   return letter, digit   Driver code str = ’geeks123pythonengineering1’ print (longestSubstring ( str )) `

Output:

` (’pythonengineering’,’ 123’) `

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