Python Regex to extract maximum numeric value from a string

Given an alphanumeric string, extract maximum numeric value from that string. Alphabets will only be in lower case. Examples:

Input : 100klh564abc365bg
Output : 564
Maximum numeric value among 100, 564 
and 365 is 564.

Input : abchsd0sdhs
Output : 0

This problem has existing solution please refer Extract maximum numeric value from a given string | Set 1 (General approach) link. We will solve this problem quickly in python using Regex. Approach is very simple,

1. Find list of all integer numbers in string separated by lower case characters using re.findall(expression,string) method.
2. Convert each number in form of string into decimal number and then find max of it.

Implementation:

Python

# Function to extract maximum numeric value from
# a given string
import re

def extractMax(input):

     # get a list of all numbers separated by
     # lower case characters
     # \d+ is a regular expression which means
     # one or more digit
     # output will be like ['100','564','365']
     numbers = re.findall('\d+',input)

     # now we need to convert each number into integer
     # int(string) converts string into integer
     # we will map int() function onto all elements
     # of numbers list
     numbers = map(int,numbers)

     print max(numbers)

# Driver program
if __name__ == "__main__":
    input = '100klh564abc365bg'
    extractMax(input)

Output

564

Time complexity : O(n), where n is the length of the input string. This is because the function iterates through the input string once to find all the numbers using the regular expression, and then iterates through the numbers again to convert them to integers.

Space complexity :  O(n)

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