Given a String, extract characters only which lie between given letters.
Input : test_str = ‘geekforLazyroar is best’, strt, end = “g”, “s”
Output : gkorgksiss
Explanation : All characters after g and before s are retained.
Input : test_str = ‘geekforLazyroar is best’, strt, end = “g”, “r”
Output : gkorgki
Explanation : All characters after g and before r are retained.
Method #1 : Using list comprehension
In this, we check for character in range using comparison operation and list comprehension does task of iteration and creation of new list. Then join() can be employed to reconvert to string.
Python3
# Python3 code to demonstrate working of # Extract range characters from String# Using list comprehension# initializing stringtest_str = 'geekforLazyroar is best'# printing original stringprint("The original string is : " + str(test_str))# initializing range letters strt, end = "f", "s"# join() to get result in string res = ''.join([chr for chr in test_str if chr >= strt and chr <= end])# printing result print("Extracted String : " + str(res)) |
The original string is : geekforLazyroar is best Extracted String : gkforgksiss
Method #2 : Using filter() + lambda + join()
Another way to solve this, in this, we perform task of comparison using lambda, and filter() used lambda function to get required characters.
Python3
# Python3 code to demonstrate working of # Extract range characters from String# Using filter() + lambda + join()# initializing stringtest_str = 'geekforLazyroar is best'# printing original stringprint("The original string is : " + str(test_str))# initializing range letters strt, end = "f", "s"# join() to get result in string res = ''.join(list(filter(lambda chr : chr >= strt and chr <= end, test_str)))# printing result print("Extracted String : " + str(res)) |
The original string is : geekforLazyroar is best Extracted String : gkforgksiss
The Time and Space Complexity for all the methods are the same:
Time Complexity: O(n)
Space Complexity: O(n)
METHOD 3:Using re
APPROACH:
This program extracts a range of characters from a given string using regular expression and the findall() function.
ALGORITHM:
Initialize the original string and print it. Define the range of characters to extract. Define a regular expression pattern to match the characters within the given range. Use the findall() function with the pattern and the original string to extract all matches. Join the matches to form the extracted string. Print the extracted string.
Python3
import re# initializing stringtest_str = 'geekforLazyroar is best'# printing original stringprint("The original string is : " + str(test_str))# initializing range lettersstrt, end = "f", "s"# pattern to match characters within rangepattern = re.compile(f'[{strt}-{end}]')# using findall() to extract all matchesmatches = pattern.findall(test_str)# joining the matches to get the extracted stringres = ''.join(matches)# printing resultprint("Extracted String : " + str(res)) |
The original string is : geekforLazyroar is best Extracted String : gkforgksiss
Time Complexity: The time complexity of this program depends on the length of the input string and the size of the character range. The findall() function has a time complexity of O(n), where n is the length of the input string. The join() function also has a time complexity of O(n), where n is the length of the resulting string. Overall, the time complexity of this program can be considered as O(n).
Space Complexity: The space complexity of this program depends on the length of the input string and the size of the character range. The program uses a regular expression pattern and a list to store the matches. The space complexity of the regular expression pattern is constant. The space complexity of the list is O(m), where m is the number of matches. Therefore, the space complexity of this program can be considered as O(m).
