Given a string, extract all the alphanumerics before 1st occurrence of non-alphanumeric.
Input : test_str = ‘geek$s4g!!!eeks’
Output : geek
Explanation : Stopped at $ occurrence.Input : test_str = ‘ge)eks4g!!!eeks’
Output : ge
Explanation : Stopped at ) occurrence.
Method #1 : Using regex + search()
In this, search() is used to search appropriate regex() for alphanumerics, then the result is sliced till 1st occurrence of a non-alphanumeric character
Python3
# Python3 code to demonstrate working of # Extract string till first Non-Alphanumeric character# Using regex + search()import re# initializing stringtest_str = 'Lazyroar4g!!!eeks'# printing original stringprint("The original string is : " + str(test_str))# using start() to get 1st substringres = re.search(r'\W+', test_str).start()res = test_str[0 : res] # printing result print("The resultant string : " + str(res)) |
The original string is : Lazyroar4g!!!eeks The resultant string : Lazyroar4g
Time Complexity: O(n)
Auxiliary Space: O(n)
Method #2 : Using findall()
This is yet another regex way to solve this problem. In this, we extract the 1st substring before non-alnum character by accessing the 0th index.
Python3
# Python3 code to demonstrate working of # Extract string till first Non-Alphanumeric character# Using findall()import re# initializing stringtest_str = 'Lazyroar4g!!!eeks'# printing original stringprint("The original string is : " + str(test_str))# using findall() to get all substrings # 0th index gives 1st substringres = re.findall("[\dA-Za-z]*", test_str)[0] # printing result print("The resultant string : " + str(res)) |
The original string is : Lazyroar4g!!!eeks The resultant string : Lazyroar4g
Time Complexity: O(n)
Auxiliary Space: O(n)
Method #3 : Using for loops
Approach
- Initiate a for loop to access characters of string
- If the character is not alphanumeric append characters to output string
- If the character is alphanumeric break the loop
- Display the output string
Python3
# Python3 code to demonstrate working of# Extract string till first Non-Alphanumeric character# initializing stringtest_str = 'Lazyroar4g!!!eeks'# printing original stringprint("The original string is : " + str(test_str))alphabets="abcdefghijklmnopqrstuvwxyz"digits="0123456789"res=""for i in test_str: if i not in alphabets+digits: break else: res+=i# printing resultprint("The resultant string : " + str(res)) |
The original string is : Lazyroar4g!!!eeks The resultant string : Lazyroar4g
Time Complexity : O(N)
Auxiliary Space : O(N)
Method #4: Using string slicing
This method uses a for loop to iterate through the characters in the string, and checks if each character is alphanumeric using the isalnum() method. If it encounters a non-alphanumeric character, it extracts the substring of the original string up to that character using string slicing (test_str[:i]). If there are no non-alphanumeric characters in the string, it simply returns the original string.
Python3
# Python3 code to demonstrate working of# Extract string till first Non-Alphanumeric character# initializing stringtest_str = 'Lazyroar4g!!!eeks'# printing original stringprint("The original string is : " + str(test_str))# Method #4: Using string slicingfor i in range(len(test_str)): if not test_str[i].isalnum(): res = test_str[:i] breakelse: res = test_str# printing resultprint("The resultant string : " + str(res)) |
The original string is : Lazyroar4g!!!eeks The resultant string : Lazyroar4g
Time Complexity : O(N), where N is length of test_str
Auxiliary Space : O(N)
Method#5: Using Recursive method.
This implementation uses a recursive function extract_string that takes in a string as input and returns the extracted string. If the input string is empty or the first character is non-alphanumeric, it returns an empty string. Otherwise, it returns the first character concatenated with the result of calling the function recursively with the remaining substring.
Python3
# Python3 code to demonstrate working of# Extract string till first Non-Alphanumeric characterdef extract_string(string): if not string or not string[0].isalnum(): return "" return string[0] + extract_string(string[1:])# initializing stringtest_str = 'Lazyroar4g!!!eeks'# printing original stringprint("The original string is : " + str(test_str))res = extract_string(test_str)# printing resultprint("The resultant string : " + str(res)) |
The original string is : Lazyroar4g!!!eeks The resultant string : Lazyroar4g
Note that this implementation can be inefficient for very long input strings, as it creates a new substring on each recursive call.
The time complexity is O(n) where n is the length of the input string.
The space complexity is also O(n) due to the recursive call stack.
