Python | Find the longest sequence of letters and numbers

find | Python functions | Regular Expressions

Michael Zippo 18.07.2021

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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Python | Find the longest sequence of letters and numbers

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